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MNC php interview questions and answers

1) what is session_set_save_handler in PHP? session_set_save_handler() sets the user-level session storage functions which are used for storing and retrieving data associated with a session. This is most useful when a storage method other than those supplied by PHP sessions is preferred. i.e. Storing the session data in a local database.

2) what is garbage collection? default time ? refresh time? Garbage Collection is an automated part of PHP , If the Garbage Collection process runs, it then analyzes any files in the /tmp for any session files that have not been accessed in a certain amount of time and physically deletes them. arbage Collection process only runs in the default session save directory, which is /tmp. If you opt to save your sessions in a different directory, the Garbage Collection process will ignore it. the Garbage Collection process does not differentiate between which sessions belong to whom when run. This is especially important note on shared web servers. If the process is run, it deletes ALL files that have not been accessed in the directory.

There are 3 PHP.ini variables, which deal with the garbage collector: PHP ini  value

name                                          default

session.gc_maxlifetime     1440 seconds or 24 minutes

session.gc_probability      1

session.gc_divisor              100

3) PHP how to know user has read the email? Using Disposition-Notification-To: in mailheader we can get read receipt.

Add the possibility to define a read receipt when sending an email.

It’s quite straightforward, just edit email.php, and add this at vars definitions:

var $readReceipt = null;

And then, at ‘createHeader’ function add:

if (!empty($this->readReceipt)) { $this->__header .= ‘Disposition-Notification-To: ‘ . $this->__formatAddress($this->readReceipt) . $this->_newLine; }

4) Runtime library loading ? without default mysql support, how to run mysql with php?

dl — Loads a PHP extension at runtime int dl ( string $library )

Loads the PHP extension given by the parameter library .

Use extension_loaded() to test whether a given extension is already available or not. This works on both built-in extensions and dynamically loaded ones (either through php.ini or dl()).

bool extension_loaded ( string $name ) — Find out whether an extension is loaded

Warning :This function has been removed from some SAPI’s in PHP 5.3.

5) what is XML-RPC ? XML-RPC is a remote procedure call protocol which uses XML to encode its calls and HTTP as a transport mechanism. An XML-RPC message is an HTTP-POST request. The body of the request is in XML. A procedure executes on the server and the value it returns is also formatted in XML.

6) default session time ? default session time in PHP is 1440 seconds or 24 minutes.

7) default session save path ? Default session save path id temporary folder /tmp

8) What is the difference between htmlentities() and htmlspecialchars()?

htmlspecialchars() – Convert some special characters to HTML entities (Only the most widely used) htmlentities() – Convert ALL special characters to HTML entities

9) how to do session using DB?

bool session_set_save_handler ( callback $open , callback $close , callback $read , callback $write , callback $destroy , callback $gc ) using this function we can store sessions in DB.

PHP has a built-in ability to override its default session handling. The function session_set_save_handler() lets the programmer specify which functions should actually be called when it is time to read or write session information. by overriding the default functions using session_set_save_handler handle we can store session in Db like below example

class SessionManager {

var $life_time;

function SessionManager() {

// Read the maxlifetime setting from PHP $this->life_time = get_cfg_var(“session.gc_maxlifetime”);

// Register this object as the session handler session_set_save_handler( array( &$this, “open” ), array( &$this, “close” ), array( &$this, “read” ), array( &$this, “write”), array( &$this, “destroy”), array( &$this, “gc” ) );

}

function open( $save_path, $session_name ) {

global $sess_save_path;

$sess_save_path = $save_path;

// Don’t need to do anything. Just return TRUE.

return true;

}

function close() {

return true;

}

function read( $id ) {

// Set empty result $data = ”;

// Fetch session data from the selected database

$time = time();

$newid = mysql_real_escape_string($id); $sql = “SELECT `session_data` FROM `sessions` WHERE `session_id` = ‘$newid’ AND `expires` > $time”;

$rs = db_query($sql); $a = db_num_rows($rs);

if($a > 0) { $row = db_fetch_assoc($rs); $data = $row[‘session_data’];

}

return $data;

}

function write( $id, $data ) {

// Build query $time = time() + $this->life_time;

$newid = mysql_real_escape_string($id); $newdata = mysql_real_escape_string($data);

$sql = “REPLACE `sessions` (`session_id`,`session_data`,`expires`) VALUES(‘$newid’, ‘$newdata’, $time)”;

$rs = db_query($sql);

return TRUE;

}

function destroy( $id ) {

// Build query $newid = mysql_real_escape_string($id); $sql = “DELETE FROM `sessions` WHERE `session_id` = ‘$newid'”;

db_query($sql);

return TRUE;

}

function gc() {

// Garbage Collection

// Build DELETE query. Delete all records who have passed the expiration time $sql = ‘DELETE FROM `sessions` WHERE `expires` < UNIX_TIMESTAMP();’;

db_query($sql);

// Always return TRUE return true;

}

}

10) how to track user logged out or not? when user is idle ? By checking the session variable exist or not while loading th page. As the session will exist longer as till browser closes.

The default behaviour for sessions is to keep a session open indefinitely and only to expire a session when the browser is closed. This behaviour can be changed in the php.ini file by altering the line session.cookie_lifetime = 0 to a value in seconds. If you wanted the session to finish in 5 minutes you would set this to session.cookie_lifetime = 300 and restart your httpd server.

11) how to track no of user logged in ? whenever a user logs in track the IP, userID etc..and store it in a DB with a active flag while log out or sesion expire make it inactive. At any time by counting the no: of active records we can get the no: of visitors.

12) in PHP for pdf which library used?

The PDF functions in PHP can create PDF files using the PDFlib library With version 6, PDFlib offers an object-oriented API for PHP 5 in addition to the function-oriented API for PHP 4. There is also the » Panda module.

FPDF is a PHP class which allows to generate PDF files with pure PHP, that is to say without using the PDFlib library. F from FPDF stands for Free: you may use it for any kind of usage and modify it to suit your needs.

FPDF requires no extension (except zlib to activate compression and GD for GIF support) and works with PHP4 and PHP5.

13) for image work which library?

You will need to compile PHP with the GD library of image functions for this to work. GD and PHP may also require other libraries, depending on which image formats you want to work with.

14) what is oops? encapsulation? abstract class? interface?

Object oriented programming language allows concepts such as modularity, encapsulation, polymorphism and inheritance.

Encapsulation passes the message without revealing the exact functional details of the class. It allows only the relevant information to the user without revealing the functional mechanism through which a particular class had functioned.

Abstract class is a template class that contains such things as variable declarations and methods, but cannot contain code for creating new instances. A class that contains one or more methods that are declared but not implemented and defined as abstract. Abstract class: abstract classes are the class where one or more methods are abstract but not necessarily all method has to be abstract. Abstract methods are the methods, which are declare in its class but not define. The definition of those methods must be in its extending class.

Interface: Interfaces are one type of class where all the methods are abstract. That means all the methods only declared but not defined. All the methods must be define by its implemented class.

15) what is design pattern? singleton pattern?

A design pattern is a general reusable solution to a commonly occurring problem in software design.

The Singleton design pattern allows many parts of a program to share a single resource without having to work out the details of the sharing themselves.

16) what are magic methods?

Magic methods are the members functions that is available to all the instance of class Magic methods always starts with “__”. Eg. __construct All magic methods needs to be declared as public To use magic method they should be defined within the class or program scope Various Magic Methods used in PHP 5 are: __construct() __destruct() __set() __get() __call() __toString() __sleep() __wakeup() __isset() __unset() __autoload() __clone()

17) what is magic quotes? Magic Quotes is a process that automagically escapes incoming data to the PHP script. It’s preferred to code with magic quotes off and to instead escape the data at runtime, as needed. This feature has been DEPRECATED as of PHP 5.3.0 and REMOVED as of PHP 6.0.0. Relying on this feature is highly discouraged.

18) diff b/w php4 & php5 ? In PHP5 1 Implementation of exceptions and exception handling

2. Type hinting which allows you to force the type of a specific argument as object, array or NULL

3. Overloading of methods through the __call function

4. Full constructors and destructors etc through a __constuctor and __destructor function

5. __autoload function for dynamically including certain include files depending on the class you are trying to create.

6 Finality : can now use the final keyword to indicate that a method cannot be overridden by a child. You can also declare an entire class as final which prevents it from having any children at all.

7 Interfaces & Abstract Classes

8 Passed by Reference : In PHP4, everything was passed by value, including objects. This has changed in PHP5 — all objects are now passed by reference.

9 An __clone method if you really want to duplicate an object

19) in php4 can you define a class? how to call class in php4? can you create object in php4?

yes you can define class and can call class by creating object of that class. but the diff b/w php4 & php5 is that in php4 everything was passed by value where as in php5 its by reference. And also any value change in reference object changes the actucal value of object also. And one more thing in introduction of __clone object in PHP5 for copying the object.

20) types of error? how to set error settings at run time?

here are three basic types of runtime errors in PHP:

1. Notices: These are trivial, non-critical errors that PHP encounters while executing a script – for example, accessing a variable that has not yet been defined. By default, such errors are not displayed to the user at all – although you can change this default behaviour.

2. Warnings: These are more serious errors – for example, attempting to include() a file which does not exist. By default, these errors are displayed to the user, but they do not result in script termination.

3. Fatal errors: These are critical errors – for example, instantiating an object of a non-existent class, or calling a non-existent function. These errors cause the immediate termination of the script, and PHP?s default behaviour is to display them to the user when they take place.

by using ini_set function.

21) what is cross site scripting? SQL injection?

Cross-site scripting (XSS) is a type of computer security vulnerability typically found in web applications which allow code injection by malicious web users into the web pages viewed by other users. Examples of such code include HTML code and client-side scripts.

SQL injection is a code injection technique that exploits a security vulnerability occurring in the database layer of an application. The vulnerability is present when user input is either incorrectly filtered for string literal escape characters embedded in SQL statements or user input is not strongly typed and thereby unexpectedly executed

22) what is outerjoin? inner join?

OUTER JOIN in SQL allows us to retrieve all values in a certain table regardless of whether these values are present in other tables

An inner join requires each record in the two joined tables to have a matching record. An inner join essentially combines the records from two tables (A and B) based on a given join-predicate.

23) what is URL rewriting?

Using URL rewriting we can convert dynamic URl to static URL Static URLs are known to be better than Dynamic URLs because of a number of reasons 1. Static URLs typically Rank better in Search Engines. 2. Search Engines are known to index the content of dynamic pages a lot slower compared to static pages. 3. Static URLs are always more friendlier looking to the End Users.

along with this we can use URL rewriting in adding variables [cookies] to the URL to handle the sessions.

24) what is the major php security hole? how to avoid?

1. Never include, require, or otherwise open a file with a filename based on user input, without thoroughly checking it first. 2. Be careful with eval() Placing user-inputted values into the eval() function can be extremely dangerous. You essentially give the malicious user the ability to execute any command he or she wishes! 3. Be careful when using register_globals = ON It was originally designed to make programming in PHP easier (and that it did), but misuse of it often led to security holes 4. Never run unescaped queries 5. For protected areas, use sessions or validate the login every time. 6. If you don’t want the file contents to be seen, give the file a .php extension.

25) whether PHP supports Microsoft SQL server ? The SQL Server Driver for PHP v1.0 is designed to enable reliable, scalable integration with SQL Server for PHP applications deployed on the Windows platform. The Driver for PHP is a PHP 5 extension that allows the reading and writing of SQL Server data from within PHP scripts. using MSSQL or ODBC modules we can access Microsoft SQL server.

26) what is MVC? why its been used? Model-view-controller (MVC) is an architectural pattern used in software engineering. Successful use of the pattern isolates business logic from user interface considerations, resulting in an application where it is easier to modify either the visual appearance of the application or the underlying business rules without affecting the other. In MVC, the model represents the information (the data) of the application; the view corresponds to elements of the user interface such as text, checkbox items, and so forth; and the controller manages the communication of data and the business rules used to manipulate the data to and from the model.

WHY ITS NEEDED IS 1 Modular separation of function 2 Easier to maintain 3 View-Controller separation means:

A — Tweaking design (HTML) without altering code B — Web design staff can modify UI without understanding code

27) what is framework? how it works? what is advantage?

In general, a framework is a real or conceptual structure intended to serve as a support or guide for the building of something that expands the structure into something useful. Advantages : Consistent Programming Model Direct Support for Security Simplified Development Efforts Easy Application Deployment and Maintenance

28) what is CURL?

CURL means Client URL Library

curl is a command line tool for transferring files with URL syntax, supporting FTP, FTPS, HTTP, HTTPS, SCP, SFTP, TFTP, TELNET, DICT, LDAP, LDAPS and FILE. curl supports SSL certificates, HTTP POST, HTTP PUT, FTP uploading, HTTP form based upload, proxies, cookies, user+password authentication (Basic, Digest, NTLM, Negotiate, kerberos…), file transfer resume, proxy tunneling and a busload of other useful tricks.

CURL allows you to connect and communicate to many different types of servers with many different types of protocols. libcurl currently supports the http, https, ftp, gopher, telnet, dict, file, and ldap protocols. libcurl also supports HTTPS certificates, HTTP POST, HTTP PUT, FTP uploading (this can also be done with PHP’s ftp extension), HTTP form based upload, proxies, cookies, and user+password authentication.

29) HOW we can transfer files from one server to another server without web forms?

using CURL we can transfer files from one server to another server. ex:

Uploading file

<?php

/* http://localhost/upload.php: print_r($_POST); print_r($_FILES); */

$ch = curl_init();

$data = array(‘name’ => ‘Foo’, ‘file’ => ‘@/home/user/test.png’);

curl_setopt($ch, CURLOPT_URL, ‘http://localhost/upload.php’);

curl_setopt($ch, CURLOPT_POST, 1); curl_setopt($ch, CURLOPT_POSTFIELDS, $data);

curl_exec($ch); ?>

output:

Array ( [name] => Foo ) Array ( [file] => Array ( [name] => test.png
[type] => image/png [tmp_name] => /tmp/phpcpjNeQ [error] => 0 [size] => 279 )   )
  30) using CSS can we have a scroll to table? 
No table won't support scrolling of its data. but we can do another workaround like placing a table
 in a DIV  layer and setting the DIV css property to overflow:auto will do the trick.
  31) how to increase session time in PHP ? 
In php.ini by setting session.gc_maxlifetime and session.cookie_lifetime values
we can change the session time in PHP.   
 32) what is UI? What are the five primary user-interface components?  
 A user interface is a means for human beings to interact with computer-based "tools" and"messages".
One presumed goal is to make the user's experience productive, efficient, pleasing, and humane.
 The primary components of UIs are  a) metaphors (fundamental concepts communicated
 through words, images, sounds, etc.)
b) mental models (structure of data, functions, tasks, roles, jobs, and people in organizations of work
and/or play)
 c) navigation (the process of moving through the mental models)
d) interaction (all input-output sequences and means for conveying feedback)
 e) and appearance (visual, verbal, acoustic, etc.).
33) How can I set a cron and how can I execute it in Unix, Linux, and windows?

Cron is very simply a Linux module that allows you to run commands at predetermined times or intervals.
In Windows, it’s called Scheduled Tasks. The name Cron is in fact derived from the same word from which we get the word chronology, which means order of time.
The easiest way to use crontab is via the crontab command. # crontab This command ‘edits’ the crontab.
Upon employing this command, you will be able to enter the commands that you wish to run.
My version of Linux uses the text editor vi. You can find information on using vi here.
The syntax of this file is very important – if you get it wrong, your crontab will not function properly.
The syntax of the file should be as follows: minutes hours day_of_month month day_of_week command All the variables, with the exception of the command itself, are numerical constants.
In addition to an asterisk (*), which is a wildcard that allows any value, the ranges permitted for each field are as follows: Minutes: 0-59 Hours: 0-23 Day_of_month: 1-31 Month: 1-12 Weekday: 0-6 We can also include multiple values for each entry, simply by separating each value with a comma.
command can be any shell command and, as we will see momentarily, can also be used to execute a Web document such as a PHP file. So, if we want to run a script every Tuesday morning at 8:15 AM, our mycronjob file will contain the following content on a single line: 15 8 * * 2 /path/to/scriptname This all seems simple enough, right? Not so fast! If you try to run a PHP script in this manner, nothing will happen (barring very special configurations that have PHP compiled as an executable, as opposed to an Apache module).
The reason is that, in order for PHP to be parsed, it needs to be passed through Apache. In other words, the page needs to be called via a browser or other means of retrieving Web content.
For our purposes, I’ll assume that your server configuration includes wget, as is the case with most default configurations. To test your configuration, log in to shell.
If you’re using an RPM-based system (e.g. Redhat or Mandrake), type the following: # wget help If you are greeted with a wget package identification, it is installed in your system.
You could execute the PHP by invoking wget on the URL to the page, like so: # wget http://www.example.com/file.php Now, let’s go back to the mailstock.php file we created in the first part of this article.
We saved it in our document root, so it should be accessible via the Internet. Remember that we wanted it to run at 4PM Eastern time, and send you your precious closing bell report? Since I’m located in the Eastern timezone, we can go ahead and set up our crontab to use 4:00, but if you live elsewhere, you might have to compensate for the time difference when setting this value.
This is what my crontab will look like: 0 4 * * 1,2,3,4,5 wget http://www.example.com/mailstock.php
34)Difference b/w OOPS concept in php4 and PHP5 ?
version 4’s object-oriented functionality was rather hobbled. Although the very basic premises of objectoriented programming (OOP) were offered in version 4, several deficiencies existed, including: • An unorthodox object-referencing methodology • No means for setting the scope (public, private, protected, abstract) of fields and methods • No standard convention for naming constructors • Absence of object destructors • Lack of an object-cloning feature • Lack of support for interfaces
35) Difference b/w MyISAM and InnoDB in MySQL?
Ans:

  • The big difference between MySQL Table Type MyISAM and InnoDB is that InnoDB supports transaction
  • InnoDB supports some newer features: Transactions, row-level locking, foreign keys
  • InnoDB is for high volume, high performance
  • use MyISAM if they need speed and InnoDB for data integrity.
  • InnoDB has been designed for maximum performance when processing large data volumes
  • Even though MyISAM is faster than InnoDB
  • InnoDB supports transaction. You can commit and rollback with InnoDB but with MyISAM once you issue a command it’s done
  • MyISAM does not support foreign keys where as InnoDB supports
  • Fully integrated with MySQL Server, the InnoDB storage engine maintains its own buffer pool for caching data and indexes in main memory. InnoDB stores its tables and indexes in a tablespace, which may consist of several files (or raw disk partitions). This is different from, for example, MyISAM tables where each table is stored using separate files. InnoDB tables can be of any size even on operating systems where file size is limited to 2GB.
  • 36) how to set session tiem out at run time or how to extend the session timeout at runtime?
    Ans:
    Sometimes it is necessary to set the default timeout period for PHP. To find out what the default (file-based-sessions) session timeout value on the server is you can view it through a ini_get command:

    // Get the current Session Timeout Value
    $currentTimeoutInSecs = ini_get(’session.gc_maxlifetime’);

    Change the Session Timeout Value

    // Change the session timeout value to 30 minutes
    ini_set(’session.gc_maxlifetime’, 30*60);

    If you have changed the sessions to be placed inside a Database occasionally implementations will specify the expiry manually. You may need to check through the session management class and see if it is getting the session timeout value from the ini configuration or through a method parameter (with default). It may require a little hunting about.

    Categories
    PHP

    AJAX Interview Questions and Answers

    What’s AJAX?
    AJAX (Asynchronous JavaScript and XML) is a newly coined term for two powerful browser features that have been around for years, but were overlooked by many web developers until recently when applications such as Gmail, Google Suggest, and Google Maps hit the streets.
    Asynchronous JavaScript and XML, or Ajax (pronounced “Aye-Jacks”), is a web development technique for creating interactive web applications using a combination of XHTML (or HTML) and CSS for marking up and styling information. (XML is commonly used, although any format will work, including preformatted HTML, plain text, JSON and even EBML).
    The Document Object Model manipulated through JavaScript to dynamically display and interact with the information presented
    The XMLHttpRequest object to exchange data asynchronously with the web server. In some Ajax frameworks and in some situations, an IFrame object is used instead of the XMLHttpRequest object to exchange data with the web server.
    Like DHTML, LAMP, or SPA, Ajax is not a technology in itself, but a term that refers to the use of a group of technologies together. In fact, derivative/composite technologies based substantially upon Ajax, such as AFLAX, are already appearing.
    Ajax applications are mostly executed on the user’s computer; they can perform a number of tasks without their performance being limited by the network. This permits the development of interactive applications, in particular reactive and rich graphic user interfaces.
    Ajax applications target a well-documented platform, implemented by all major browsers on most existing platforms. While it is uncertain that this compatibility will resist the advent of the next generations of browsers (in particular, Firefox), at the moment, Ajax applications are effectively cross-platform.
    While the Ajax platform is more restricted than the Java platform, current Ajax applications effectively fill part of the one-time niche of Java applets: extending the browser with portable, lightweight mini-applications.
    Ajax isn’t a technology. It’s really several technologies, each flourishing in its own right, coming together in powerful new ways. Ajax incorporates:
    * standards-based presentation using XHTML and CSS;
    * dynamic display and interaction using the Document Object Model;
    * data interchange and manipulation using XML and XSLT; * asynchronous data retrieval using XMLHttpRequest;
    * and JavaScript binding everything together.
    Who’s Using Ajax ?
    Google is making a huge investment in developing the Ajax approach. All of the major products Google has introduced over the last year ? Orkut, Gmail, the latest beta version of Google Groups, Google Suggest, and Google Maps ? are Ajax applications. (For more on the technical nuts and bolts of these Ajax implementations, check out these excellent analyses of Gmail, Google Suggest, and Google Maps.) Others are following suit: many of the features that people love in Flickr depend on Ajax, and Amazon?s A9.com search engine applies similar techniques.
    These projects demonstrate that Ajax is not only technically sound, but also practical for real-world applications. This isn?t another technology that only works in a laboratory. And Ajax applications can be any size, from the very simple, single-function Google Suggest to the very complex and sophisticated Google Maps.
    Who’s Using Ajax ?
    Google is making a huge investment in developing the Ajax approach. All of the major products Google has introduced over the last year ? Orkut, Gmail, the latest beta version of Google Groups, Google Suggest, and Google Maps ? are Ajax applications. (For more on the technical nuts and bolts of these Ajax implementations, check out these excellent analyses of Gmail, Google Suggest, and Google Maps.) Others are following suit: many of the features that people love in Flickr depend on Ajax, and Amazon?s A9.com search engine applies similar techniques.
    These projects demonstrate that Ajax is not only technically sound, but also practical for real-world applications. This isn?t another technology that only works in a laboratory. And Ajax applications can be any size, from the very simple, single-function Google Suggest to the very complex and sophisticated Google Maps.
    At Adaptive Path, we?ve been doing our own work with Ajax over the last several months, and we?re realizing we?ve only scratched the surface of the rich interaction and responsiveness that Ajax applications can provide. Ajax is an important development for Web applications, and its importance is only going to grow. And because there are so many developers out there who already know how to use these technologies, we expect to see many more organizations following Google?s lead in reaping the competitive advantage Ajax provides.
    Moving Forward
    The biggest challenges in creating Ajax applications are not technical. The core Ajax technologies are mature, stable, and well understood. Instead, the challenges are for the designers of these applications: to forget what we think we know about the limitations of the Web, and begin to imagine a wider, richer range of possibilities
    Should I consider AJAX?
    AJAX definitely has the buzz right now, but it might not be the right thing for you. AJAX is limited to the latest browsers, exposes browser compatibility issues, and requires new skill-sets for many. There is a good blog entry by Alex Bosworth on AJAX Mistakes which is a good read before you jump full force into AJAX.
    On the other hand you can achieve highly interactive rich web applications that are responsive and appear really fast. While it is debatable as to whether an AJAX based application is really faster, the user feels a sense of immediacy because they are given active feedback while data is exchanged in the background. If you are an early adopter and can handle the browser compatibility issues, and are willing to learn some more skills, then AJAX is for you. It may be prudent to start off AJAX-ifying a small portion or component of your application first. We all love technology, but just remember the purpose of AJAX is to enhance your user’s experience and not hinder it.
    Does AJAX work with Java?
    Absolutely. Java is a great fit for AJAX! You can use Java Enterprise Edition servers to generate AJAX client pages and to serve incoming AJAX requests, manage server side state for AJAX clients, and connect AJAX clients to your enterprise resources. The JavaServer Faces component model is a great fit for defining and using AJAX components.
    Won’t my server-side framework provide me with AJAX?
    You may be benefiting from AJAX already. Many existing Java based frameworks already have some level of AJAX interactions and new frameworks and component libraries are being developed to provide better AJAX support. I won’t list all the Java frameworks that use AJAX here, out of fear of missing someone, but you can find a good list at www.ajaxpatterns.org/Java_Ajax_Frameworks.
    If you have not chosen a framework yet it is recommended you consider using JavaServer Faces or a JavaServer Faces based framework. JavaServer Faces components can be created and used to abstract many of the details of generating JavaScript, AJAX interactions, and DHTML processing and thus enable simple AJAX used by JSF application developer and as plug-ins in JSF compatible IDE’s, such as Sun Java Studio Creator.
    Where should I start?
    Assuming the framework you are using does not suffice your use cases and you would like to develop your own AJAX components or functionality I suggest you start with the article Asynchronous JavaScript Technology and XML (AJAX) With Java 2 Platform, Enterprise Edition.
    If you would like to see a very basic example that includes source code you can check out the tech tip Using AJAX with Java Technology. For a more complete list of AJAX resources the Blueprints AJAX home page.
    Next, I would recommend spending some time investigating AJAX libraries and frameworks. If you choose to write your own AJAX clients-side script you are much better off not re-inventing the wheel.
    AJAX in Action by Dave Crane and Eric Pascarello with Darren James is good resource. This book is helpful for the Java developer in that in contains an appendix for learning JavaScript for the Java developer.
    Did Adaptive Path invent Ajax? Did Google? Did Adaptive Path help build Google?s Ajax applications?
    Neither Adaptive Path nor Google invented Ajax. Google?s recent products are simply the highest-profile examples of Ajax applications. Adaptive Path was not involved in the development of Google?s Ajax applications, but we have been doing Ajax work for some of our other clients.
    Is it possible to set session variables from javascript?
    It’s not possible to set any session variables directly from javascript as it is purely a client side technology. You can use AJAX though to asyncronously…
    Cannot parse XML generated by JSP I am generating an XML using JSP, when i run the JSP in IE it shows the XML as per DOM, but when i try to parse it using Javascript , the command xmldoc.documentElement…
    This is working code I am using, it might help you. if (!isIE) xmldoc = req.responseXML; else { //IE does not take the responseXML as…
    What do I need to know to create my own AJAX functionality?
    If you plan not to reuse and existing AJAX component here are some of the things you will need to know.
    Plan to learn Dynamic HTML (DHTML), the technology that is the foundation for AJAX. DHTML enables browser-base real time interaction between a user and a web page. DHTML is the combination of JavaScript, the Document Object Model (DOM) and Cascading Style Sheets (CSS).
    * JavaScript – JavaScript is a loosely typed object based scripting language supported by all major browsers and essential for AJAX interactions. JavaScript in a page is called when an event in a page occurs such as a page load, a mouse click, or a key press in a form element.
    * DOM – An API for accessing and manipulating structured documents. In most cases DOM represent the structure of XML and HTML documents.
    * CSS – Allows you to define the presentation of a page such as fonts, colors, sizes, and positioning. CSS allow for a clear separation of the presentation from the content and may be changed programmatically by JavaScript.
    Understanding the basic request/response nature of HTTP is also important. Many subtle bugs can result if you ignore the differences between the GET and OIst methods when configuring an XMLHttpRequest and HTTP response codes when processing callbacks.
    JavaScript is the client-side glue, in a sense. JavaScript is used to create the XMLHttpRequest Object and trigger the asynchronous call. JavaScript is used to parse the returned content. JavaScript is used to analyze the returned data and process returned messages. JavaScript is used to inject the new content into the HTML using the DOM API and to modify the CSS.
    Do I really need to learn JavaScript?
    Basically yes if you plan to develop new AJAX functionality for your web application.
    On the other hand, JSF components and component libraries can abstract the details of JavaScript, DOM and CSS. These components can generate the necessary artifacts to make AJAX interactions possible. Visual tools such as Java Studio Creator may also use AJAX enabled JSF components to create applications, shielding the tool developer from many of the details of
    AJAX. If you plan to develop your own JSF components or wire the events of components together in a tool it is important that you have a basic understanding of JavaScript. There are client-side JavaScript libraries (discussed below) that you can call from your in page JavaScript that abstract browser differences. Object Hierarchy and Inheritance in JavaScript is a great resource for a Java developer to learn about JavaScript objects.
    Do Ajax applications always deliver a better experience than traditional web applications?
    Not necessarily. Ajax gives interaction designers more flexibility. However, the more power we have, the more caution we must use in exercising it. We must be careful to use Ajax to enhance the user experience of our applications, not degrade it.
    What JavaScript libraries and frameworks are available?
    There are many libraries/frameworks out there (and many more emerging) that will help abstract such things as all the nasty browser differences. Three good libraries are The Dojo Toolkit, Prototype, and DWR.
    * The Dojo Toolkit contains APIs and widgets to support the development of rich web applications. Dojo contains an intelligent packaging system, UI effects, drag and drop APIs, widget APIs, event abstraction, client storage APIs, and AJAX interaction APIs. Dojo solves common usability issues such as support for dealing with the navigation such as the ability to detect the browser back button, the ability to support changes to the URL in the URL bar for bookmarking, and the ability to gracefully degrade when AJAX/JavaScript is not fully support on the client. Dojo is the Swiss Army Knife of JavaScript libraries. It provides the widest range of options in a single library and it does a very good job supporting new and older browsers.
    * Prototype focuses on AJAX interactions including a JavaScript AJAX object that contains a few objects to do basic tasks such as make a request, update a portion of a document, insert content into a document, and update a portion of a document periodically. Prototype JavaScript library contains a set of JavaScript objects for representing AJAX requests and contains utility functions for accessing in page components and DOM manipulations. Script.aculo.us and Rico are built on top of Prototype and provide UI effects, support for drag and drop, and include common JavaScript centric widgets. If you are just looking to support AJAX interactions and a few basic tasks Prototype is great. If you are looking for UI effects Rico and Script.aculo.us are good options.
    * Yahoo UI Library is a utility library and set of widgets using the APIs to support rich clients. The utility library includes support for cross-browser AJAX interactions, animation, DOM scriptging support, drag and drop, and cross browser event support. The Yahoo UI Library is well documnented and contains many examples.
    * DWR (Dynamic Web Remoting) is a client-side and server-side framework that focuses on allowing a developer to do RPC calls from client-side JavaScript to plain old Java objects in a Java Enterprise Edition web container. On the server side DWR uses a Servlet to interact with the Java objects and returns object representations of the Java objects or XML documents. DWR will be easy to get up and running and plays well with other Java technologies. If you are looking for a client-side and server-side framework that integrates well use DWR.
    * Google Web Toolkit (GWT) is client/server framework provided by Google that allows a developer to write an AJAX application in pure Java. The GWT takes care of the details of generating all the client-side code using a Java-to-JavaScript compiler. One of the key benefits of the GWT Software Developer Kit (SDK) is that it allows you to debug your applications in what is known as GWT hosted mode using an embedded browser (IE on Windows and Mozilla/Gecko on Linux) that is tied to the toolkit. In GWT hosted mode you setup through the code and debug it as it is running on both the client and server. The GWT contains a default set of widgets and widget containers. An application is built by coding a set of widgets and containers together much like would be done in a Swing application. The GWT Software Developer Kit (SDK) is limited to Linux and Windows XP/2000 though the web applications it generates are compatible with the latest generation of the mainstream browsers.
    There are many new and emerging libraries for JavaScript and this list only reviews some of the more common libraries. When making a choice choose the library which suites your needs the best. While it might be better to choose one, there is nothing stopping you from using more than one framework. For a more extensive list of client-side frameworks see: Survey of AJAX/JavaScript Libraries.
    What is the difference between proxied and proxyless calls?
    Proxied calls are made through stub objects that mimic your PHP classes on the JavaScript side. E.g., the helloworld class from the Hello World example.
    Proxyless calls are made using utility javascript functions like HTML_AJAX.replace() and HTML_AJAX.append().
    Should I use XML or text, JavaScript, or HTML as a return type?
    It depends. Clearly the ‘X’ in AJAX stands for XML, but several AJAX proponents are quick to point out that nothing in AJAX, per se, precludes using other types of payload, such as, JavaScript, HTML, or plain text.
    * XML – Web Services and AJAX seem made for one another. You can use client-side API’s for downloading and parsing the XML content from RESTful Web Services. (However be mindful with some SOAP based Web Services architectures the payloads can get quite large and complex, and therefore may be inappropriate with AJAX techniqes.)
    * Plain Text – In this case server-generated text may be injected into a document or evaluated by client-side logic.
    * JavaScript – This is an extension to the plain text case with the exception that a server-side component passes a fragment of JavaScript including JavaScript object declarations. Using the JavaScript eval() function you can then create the objects on the client. JavaScript Object Notation (JSON), which is a JavaScript object based data exchange specification, relies on this technique.
    * HTML – Injecting server-generated HTML fragments directly into a document is generally a very effective AJAX technique. However, it can be complicated keeping the server-side component in sync with what is displayed on the client.
    Mashup is a popular term for creating a completely new web application by combining the content from disparate Web Services and other online API’s. A good example of a mashup is housingmaps.com which graphically combines housing want-ads from craiglist.org and maps from maps.google.com.
    Are there Usability Issues with AJAX?
    The nature of updating a page dynamically using data retrieved via AJAX interactions and DHTML may result in drastically changing the appearance and state of a page. A user might choose to use the browser’s back or forward buttons, bookmark a page, copy the URL from the URL bar and share it with a friend via an email or chat client, or print a page at any given time. When designing an AJAX based application you need to consider what the expected behavior would be in the case of navigation, bookmarking, printing, and browser support as described below.
    * Navigation – What would be the expected behavior of the back, forward, refresh, and bookmark browser buttons in your application design. While you could implement history manipulation manually it may be easer to use a JavaScript frameworks such as Dojo that provides API’s history manipulation and navigation control.
    * Bookmarking and URL sharing – Many users want to bookmark or cut and paste the URL from the browser bar. Dojo provides client-side for bookmarking and URL manipulation.
    * Printing – In some cases printing dynamically rendered pages can be problematic.
    Other considerations as a developer when using AJAX are:
    * Browser Support – Not all AJAX/DHTML features are supported on all browsers or all versions of a browser. See quirksmode.org for a list of browser support and possible workarounds.
    * JavaScript disabled – You should also consider what happens if the user disables JavaScript. Additionally, there are several legitimate reasons why JavaScript and CSS support may be unavailable on a user’s web browser.
    * Latency – Keep in mind latency in your design. A running application will be much more responsive than when it is deployed.
    Latency problems: myth or reality?
    * Accessibility – Guaranteeing your site is accessible to people with disabilities is not only a noble goal, it is also requited by law in many markets. Some marvelous enabling technology is available to help people use the Web in spite of disabilities including visual, auditory, physical, speech, cognitive, and neurological disabilities. With a little forethought, and comprehension of some well documented best practices, you can assure that your application is compatible with that enabling technology.
    Degradability is the term used to describe techniques used by web applications to adapt to the wide range of web browser capabilities. Many AJAX libraries have automatic degradability built in. But if you are coding your own custom AJAX functionality, simply taking some care to follow the best practices promoted by standards bodies like the World Wide Web Consortium (W3C), and grass root movements like the Web Standards community and many others, your application can run usefully on browsers that are incapable of AJAX behaviors. Granted, your application may loose some of the “wow factor” on these less capable browsers, but your application will still be usable.
    Remember to not design with AJAX just for the sake of coolness. The reason you built your application is so people will use it. And people will not use your application if your application is not compatible with their web browser.
    Are there any frameworks available to help speedup development with AJAX?
    There are several browser-side frameworks available, each with their own uniqueness…
    Is Adaptive Path selling Ajax components or trademarking the name? Where can I download it?
    Ajax isn?t something you can download. It?s an approach ? a way of thinking about the architecture of web applications using certain technologies. Neither the Ajax name nor the approach are proprietary to Adaptive Path.
    Should I use an HTTP GET or POST for my AJAX calls?
    AJAX requests should use an HTTP GET request when retrieving data where the data will not change for a given request URL. An HTTP POST should be used when state is updated on the server. This is in line with HTTP idempotency recommendations and is highly recommended for a consistent web application architecture.
    How do I debug JavaScript?
    There are not that many tools out there that will support both client-side and server-side debugging. I am certain this will change as AJAX applications proliferate. I currently do my client-side and server-side debugging separately. Below is some information on the client-side debuggers on some of the commonly used browsers.
    * Firefox/Mozilla/Netscape – Have a built in debugger Venkman which can be helpful but there is a Firefox add on known as FireBug which provides all the information and AJAX developer would ever need including the ability to inspect the browser DOM, console access to the JavaScript runtime in the browser, and the ability to see the HTTP requests and responses (including those made by an XMLHttpRequest). I tend to develop my applications initially on Firefox using Firebug then venture out to the other browsers.
    * Safari – Has a debugger which needs to be enabled. See the Safari FAQ for details.
    * Internet Explorer – There is MSDN Documentation on debugging JavaScript. A developer toolbar for Internet Explorer may also be helpful.
    While debuggers help a common technique knowing as “Alert Debugging” may be used. In this case you place “alert()” function calls inline much like you would a System.out.println. While a little primitive it works for most basic cases. Some frameworks such as Dojo provide APIs for tracking debug statements.
    How do I provide internationalized AJAX interactions?
    Just because you are using XML does not mean you can properly send and receive localized content using AJAX requests. To provide internationalized AJAX components you need to do the following:
    * Set the charset of the page to an encoding that is supported by your target languages. I tend to use UTF-8 because it covers the most languages. The following meta declaration in a HTML/JSP page will set the content type:
    * In the page JavaScript make sure to encode any parameters sent to the server. JavaScript provides the escape() function which returns Unicode escape strings in which localized text will appear in hexadecimal format. For more details on JavaScript encoding see Comparing escape(), encodeURI(), and encodeURIComponent().
    * On the server-side component set the character encoding using the HttpServletRequest.setCharacterEncoding() method. Before you access the localized parameter using the HttpServletRequest.getParameter() call. In the case of UTF this would be request.setCharactherEncoding(“UTF-8”);.
    A server-side component returning AJAX responses needs to set the encoding of the response to the same encoding used in the page.
    response.setContentType(“text/xml;charset=;UTF-8″);
    response.getWriter().write(” invalid “);
    For more information on using AJAX with Java Enterprise Edition technologies see AJAX and Internationalization and for developing multi-lingual applications see Developing Multilingual Web Applications Using JavaServer Pages Technology.
    Some of the Google examples you cite don?t use XML at all. Do I have to use XML and/or XSLT in an Ajax application?
    No. XML is the most fully-developed means of getting data in and out of an Ajax client, but there?s no reason you couldn?t accomplish the same effects using a technology like JavaScript Object Notation or any similar means of structuring data for interchange.
    Are Ajax applications easier to develop than traditional web applications?
    Not necessarily. Ajax applications inevitably involve running complex JavaScript code on the client. Making that complex code efficient and bug-free is not a task to be taken lightly, and better development tools and frameworks will be needed to help us meet that challenge.
    When do I use a synchronous versus a asynchronous request?
    Good question. They don’t call it AJAX for nothing! A synchronous request would block in page event processing and I don’t see many use cases where a synchronous request is preferable.
    How do I handle concurrent AJAX requests?
    With JavaScript you can have more than one AJAX request processing at a single time. In order to insure the proper post processing of code it is recommended that you use JavaScript Closures. The example below shows an XMLHttpRequest object abstracted by a JavaScript object called AJAXInteraction. As arguments you pass in the URL to call and the function to call when the processing is done.
    function AJAXInteraction(url, callback) {
    var req = init();
    req.onreadystatechange = processRequest;
    function init() {
    if (window.XMLHttpRequest) {
    return new XMLHttpRequest();
    } else if (window.ActiveXObject) {
    return new ActiveXObject(“Microsoft.XMLHTTP”);
    }
    }
    function processRequest () {
    if (req.readyState == 4) {
    if (req.status == 200) {
    if (callback) callback(req.responseXML);
    }
    }
    }
    this.doGet = function() {
    req.open(“GET”, url, true);
    req.send(null);
    }
    this.doPost = function(body) {
    req.open(“POST”, url, true);
    req.setRequestHeader(“Content-Type”, ”
    application/x-www-form-urlencoded”);
    req.send(body);
    }
    }
    function makeRequest() {
    var ai = new AJAXInteraction(“processme”,
    function() { alert(“Doing Post Process”);});
    ai.doGet();
    }
    The function makeRequest() in the example above creates an AJAXInteraction with a URL to of “processme” and an inline function that will show an alert dialog with the message “Doing Post Process”. When ai.doGet() is called the AJAX interaction is initiated and when server-side component mapped to the URL “processme” returns a document which is passed to the callback function that was specified when the AJAXInteraction was created.
    Using this closures insures that the proper callback function associated with a specific AJAX interaction is called. Caution should still be taken when creating multiple closure objects in that make XmlHttpRequests as to there is a limited number of sockets that are used to make requests at any given time. Because there are limited number of requests that can be made concurrently. Internet Explorer for example only allows for two concurrent AJAX requests at any given time. Other browsers may allow more but it is generally between three and five requests. You may choose to use pool of AJAXInteraction objects.
    One thing to note when making multiple AJAX calls from the client is that the calls are not guaranteed to return in any given order. Having closures within the callback of a closure object can be used to ensure dependencies are processed correctly.
    There is a discussion titled Ajaxian Fire and Forget Pattern that is helpful.
    What do I do on the server to interact with an AJAX client?
    The “Content-Type” header needs to be set to”text/xml”. In servlets this may be done using the HttpServletResponse.setContentType()should be set to “text/xml” when the return type is XML. Many XMLHttpRequest implementations will result in an error if the “Content-Type” header is set The code below shows how to set the “Content-Type”.
    response.setContentType(“text/xml”);
    response.getWriter().write(“invalid”);
    You may also want to set whether or not to set the caches header for cases such as autocomplete where you may want to notify proxy servers/and browsers not to cache the results.
    response.setContentType(“text/xml”);
    response.setHeader(“Cache-Control”, “no-cache”);
    response.getWriter().write(“invalid”);
    Note to the developer: Internet Explorer will automatically use a cached result of any AJAX response from a HTTP GET if this header is not set which can make things difficult for a developer. During development mode you may want set this header. Where do I store state with an AJAX client
    As with other browser based web applications you have a few options which include:
    * On the client in cookies – The size is limited (generally around 4KB X 20 cookies per domain so a total of 80KB) and the content may not be secure unless encrypted which is difficult but not impossible using JavaScript.
    * On the client in the page – This can be done securely but can be problematic and difficult to work with. See my blog entry on Storing State on the Client for more details on this topic.
    * On the client file system – This can be done if the client grants access to the browser to write to the local file system. Depending on your uses cases this may be necessary but caution is advised.
    * On the Server – This is closer to the traditional model where the client view is of the state on the server. Keeping the data in sync can be a bit problematic and thus we have a solution Refreshing Data on this. As more information processing and control moves to the client where state is stored will need to be re-evaluated.
    Whats with the -alpha in the install instructions?
    HTML_AJAX hasn’t had a stable release yet and the pear installer doesn’t install non stable packages by default unless you specify a version.
    How do I submit a form or a part of a form without a page refresh?
    When creating a form make sure that the “form” element “onSubmit” attribute is set to a JavaScript function that returns false.
    You can also submit data by associating a function with a form button in a similar way.
    Note that the form “onSubmit” attribute is still set. If the user hits the enter key in the text field the form will be submitted so you still need to handle that case.
    When updating the page it is recommend you wait to make sure that the AJAX update of the form data was successful before updating the data in the page. Otherwise, the data may not properly update and the user may not know. I like to provide an informative message when doing a partial update and upon a successful AJAX interaction I will then update the page.
    How do I test my AJAX code?
    There is a port of JUnit for client-side JavaScript called JsUnit
    What exactly is the W3C DOM?
    The W3C Document Object Model (DOM) is defined by the W3C as the following: The Document Object Model is a platform- and language-neutral interface…
    When will HTML_AJAX have a stable release?
    Once all the major features are complete and the API has been tested, the roadmap gives an idea of whats left to be done.
    What parts of the HTML_AJAX API are stable?
    We don’t have a list right now, but most of the API is stable as of 0.3.0. There should be no major changes at this point, though there will be lots of new additions.
    What Browsers does HTML_AJAX work with?
    As of 0.3.0, all the examples that ship with HTML_AJAX have been verified to work with
    * Firefox 1.0+
    * Internet Explorer 5.5+ (5.0 should work but it hasn’t been tested)
    Most things work with
    * Safari 2+
    * Opera 8.5+
    Is the server or the client in control?
    It depends. With AJAX the answer is more in between. Control can be more centralized in a server-side component or as a mix of client-side and server-side controllers.
    * Centralized server-side controller – When having a more centralized controller the key is to make sure the data in client-side page is in sync with that of the server. Some applications may keep all the state on the server and push all updates to client DOM via a simple JavaScript controller.
    * Client and server-side controllers – This architecture would use JavaScript to do all presentation related control, event processing, page manipulation, and rendering of model data on the client. The server-side would be responsible for things such as business logic and pushing updated model data to the client. In this case the server would not have intimate knowledge of the presentation short of the initial page that would be sent to the client page request.
    There are some use cases where an entire AJAX application can be written in a single page. Keep in mind if you choose this type of architecture that navigation and bookmarking should be considered.
    Both methods are viable depending on what you are trying to accomplish. I tend to prefer spreading the control across the client and server.
    Is Ajax just another name for XMLHttpRequest?
    No. XMLHttpRequest is only part of the Ajax equation. XMLHttpRequest is the technical component that makes the asynchronous server communication possible; Ajax is our name for the overall approach described in the article, which relies not only on XMLHttpRequest, but on CSS, DOM, and other technologies.
    How do I abort the current XMLHttpRequest?
    Just call the abort() method on the request.
    What is the minimum version of PHP that needs to be running in order to use HTML_AJAX?
    The oldest PHP version i’ve fully tested HTML_AJAX is 4.3.11, but it should run on 4.2.0 without any problems. (Testing reports from PHP versions older then 4.3.11 would be appreciated.)
    Why does HTML_AJAX hang on some server installs?
    If you run into an HTML_AJAX problem only on some servers, chances are your running into a problem with output compression. If the output compression is handled in the PHP config we detect that and do the right thing, but if its done from an apache extension we have no way of knowing its going to compress the body. Some times setting HTML_AJAX::sendContentLength to false fixes the problem, but in other cases you’ll need to disabled the extension for the AJAX pages.
    I’ve also seen problems caused by debugging extensions like XDebug, disabling the extension on the server page usually fixes that. Questions dealing with Using HTML_AJAX, and general JavaScript development
    How do I get the XMLHttpRequest object?
    Depending upon the browser… if (window.ActiveXObject) { // Internet Explorer http_request = new ActiveXObject(“Microsoft.XMLHTTP”); } else if…
    Are there any security issues with AJAX?
    JavaScript is in plain view to the user with by selecting view source of the page. JavaScript can not access the local filesystem without the user’s permission. An AJAX interaction can only be made with the servers-side component from which the page was loaded. A proxy pattern could be used for AJAX interactions with external services.
    You need to be careful not to expose your application model in such as way that your server-side components are at risk if a nefarious user to reverse engineer your application. As with any other web application, consider using HTTPS to secure the connection when confidential information is being exchanged.
    What about applets and plugins ?
    Don’t be too quick to dump your plugin or applet based portions of your application. While AJAX and DHTML can do drag and drop and other advanced user interfaces there still limitations especially when it comes to browser support. Plugins and applets have been around for a while and have been able to make AJAX like requests for years. Applets provide a great set of UI components and APIs that provide developers literally anything.
    Many people disregard applets or plugins because there is a startup time to initialize the plugin and there is no guarantee that the needed version of a plugin of JVM is installed. Plugins and applets may not be as capable of manipulating the page DOM. If you are in a uniform environment or can depend on a specific JVM or plugin version being available (such as in a corporate environment) a plugin or applet solution is great.
    One thing to consider is a mix of AJAX and applets or plugins. Flickr uses a combination of AJAX interactions/DHTML for labeling pictures and user interaction and a plugin for manipulating photos and photo sets to provide a great user experience. If you design your server-side components well they can talk to both types of clients.
    Why did you feel the need to give this a name?
    I needed something shorter than ?Asynchronous JavaScript+CSS+DOM+XMLHttpRequest? to use when discussing this approach with clients.
    Is AJAX code cross browser compatible?
    Not totally. Most browsers offer a native XMLHttpRequest JavaScript object, while another one (Internet Explorer) require you to get it as an ActiveX object….
    Techniques for asynchronous server communication have been around for years. What makes Ajax a ?new? approach?
    What?s new is the prominent use of these techniques in real-world applications to change the fundamental interaction model of the Web. Ajax is taking hold now because these technologies and the industry?s understanding of how to deploy them most effectively have taken time to develop.
    Is Ajax a technology platform or is it an architectural style?
    It?s both. Ajax is a set of technologies being used together in a particular way.
    How do I handle the back and forward buttons?
    While you could go out and create a custom solution that tracks the current state on your application I recommend you leave this to the experts. Dojo addresses the navigation in a browser neutral way as can be seen in the JavaScript example below.
    function updateOnServer(oldId, oldValue,
    itemId, itemValue) {
    var bindArgs = {
    url: “faces/ajax-dlabel-update”,
    method: “post”,
    content: {“component-id”: itemId, “component-value”:
    itemValue},
    mimetype: “text/xml”,
    load: function(type, data) {
    processUpdateResponse(data);
    },
    backButton: function() {
    alert(“old itemid was ” + oldId);
    },
    forwardButton: function(){
    alert(“forward we must go!”);
    }
    };
    dojo.io.bind(bindArgs);
    }
    The example above will update a value on the server using dojo.io.bind() with a function as a property that is responsible for dealing with the browser back button event. As a developer you are capable of restoring the value to the oldValue or taking any other action that you see fit. The underlying details of how the how the browser button event are detected are hidden from the developer by Dojo.
    AJAX: How to Handle Bookmarks and Back Buttons details this problem and provides a JavaScript library Really Simple History framework (RSH) that focuses just on the back and forward issue.
    How does HTML_AJAX compare with the XAJAX project at Sourceforge?
    XAJAX uses XML as a transport for data between the webpage and server, and you don’t write your own javascript data handlers to manipulate the data received from the server. Instead you use a php class and built in javascript methods, a combination that works very similiar to the HTML_AJAX_Action class and haSerializer combo. XAJAX is designed for simplicity and ease of use.
    HTML_AJAX allows for multiple transmission types for your ajax data – such as urlencoding, json, phpserialized, plain text, with others planned, and has a system you can use to write your own serializers to meet your specific needs. HTML_AJAX has a class to help generate javascript (HTML_AJAX_Helper) similiar to ruby on rail’s javascript helper (although it isn’t complete), and an action system similiar to XAJAX’s “action pump” that allows you to avoid writing javascript data handlers if you desire.
    But it also has the ability to write your own data handling routines, automatically register classes and methods using a server “proxy” script, do different types of callbacks including grabbing remote urls, choose between sync and async requests, has iframe xmlhttprequest emulation fallback capabilities for users with old browsers or disabled activeX, and is in active development with more features planned (see the Road Map for details)
    HTML_AJAX has additional features such as client pooling and priority queues for more advanced users, and even a javascript utility class. Although you can use HTML_AJAX the same way you use XAJAX, the additional features make it more robust, extensible and flexible. And it is a pear package, you can use the pear installer to both install and keep it up to date.
    If you’re asking which is “better” – as with most php scripts it’s a matter of taste and need. Do you need a quick, simple ajax solution? Or do you want something that’s flexible, extensible, and looking to incorporate even more great features? It depends on the project, you as a writer, and your future plans.
    What browsers support AJAX?
    Internet Explorer 5.0 and up, Opera 7.6 and up, Netscape 7.1 and up, Firefox 1.0 and up, Safari 1.2 and up, among others.
    How do I send an image using AJAX?
    While it may appear that images are being sent when using AJAX with an application like Google Maps what is really happening is that the URLs of images are being send as the response of an AJAX request and those URLs are being set using DHTML.
    In this example an XML document is returned from an AJAX interaction and the category bar is populated.
    1
    Books
    Fun to read
    books_icon.gif
    2
    Electronics
    Must have gadgets
    electronics.gif
    Notice that the image-url element contains the location of the URL for the image representing a category. The callback method of an AJAX interaction will parse the response XML document and call the addCategory function for each category included in the response XML document. The addCategory function looks up a table row element “categoryTable” in body of the page and adds a row to the element which contains the image.

    function addCategory(id, name, imageSrc) {
    var categoryTable = document.getElementById(“categoryTable”);
    var row = document.createElement(“tr”);
    var catCell = document.createElement(“td”);
    var img = document.createElement(“img”);
    img.src = (“images\\” + imageSrc);
    var link = document.createElement(“a”);
    link.className =”category”;
    link.appendChild(document.createTextNode(name));
    link.setAttribute(“onclick”, “catalog?command=category&catid=” + id);
    catCell.appendChild(img);
    catCell.appendChild(link);
    row.appendChild(catCell);
    categoryTable.appendChild(row);
    }

      Body Here

    Note that the source of the image is set to the image source. The image is loaded by a subsequent HTTP request for the image at the URL “images/books_icon.gif” or “images/electronic_icon.gif” that occurs when the img element is added to the categoryTable.
    Will HTML_AJAX integrate with other Javascript AJAX libraries such as scriptaculous ? How would this integration look like?
    HTML_AJAX doesn’t have specific plans to integrate with other JavaScript libraries. Part of this is because external dependencies make for a more complicated installation process. It might make sense to offer some optional dependencies on a library like scriptaculous automatically using its visual effects for the loading box or something, but there isn’t a lot to gain from making default visuals like that flashier since they are designed to be easily replaceable.
    Most integration would take place in higher level components. Its unclear whether higher level components like that should be part of HTML_AJAX delivered through PEAR or if they should just be supported by HTML_AJAX and made available from http://htmlajax.org or some other site. If your interested in building widgets or components based on HTML_AJAX please let me know.
    HTML_AJAX does however offer the ability to use its library loading mechanism with any JavaScript library. I use scriptaculous in conjunction with HTML_AJAX and I load both libraries through the server.
    To do this you just need to register the library with your server and load add its flag to your include line.
    server->registerJSLibrary(‘scriptaculous’,
    array(‘prototype.js’,’scriptaculous.js’,’builder.js’,’effects.js’,’dragdrop.js’,’controls.js’,’slider.js’), ‘/pathto/scriptaculous/’);?>
    When should I use an Java applet instead of AJAX?
    Applets provide a rich experience on the client side and there are many things they can do that an AJAX application cannot do, such as custom data streaming, graphic manipulation, threading, and advanced GUIs. While DHTML with the use of AJAX has been able to push the boundaries on what you can do on the client, there are some things that it just cannot do. The reason AJAX is so popular is that it only requires functionality built into the browser (namely DHTML and AJAX capabilities). The user does not need to download and/or configure plugins. It is easy to incrementally update functionality and know that that functionality will readily available, and there are not any complicated deployment issues. That said, AJAX-based functionality does need to take browser differences into consideration. This is why we recommend using a JavaScript library such as Dojo which abstracts browser differences. So the “bottom line” is: If you are creating advanced UIs where you need more advanced features on the client where you want UI accuracy down to the pixel, to do complex computations on the client, use specialized networking techniques, and where you know that the applet plugin is available for your target audience, applets are the way to go. AJAX/DHTML works well for applications where you know the users are using the latest generation of browsers, where DHTML/AJAX “good enough” for you, and where your developers have JavaScript/DHTML/AJAX skills. Many amazing things can be done with AJAX/DHTML but there are limitations. AJAX and applets can be used together in the same UIs with AJAX providing the basic structure and applets providing more advanced functionality. The Java can communicate to JavaScript using the Live-Connect APIs. The question should not be should framed as do I use AJAX or applets, but rather which technology makes the best sense for what you are doing. AJAX and applets do not have to be mutually exclusive.
    What kinds of applications is Ajax best suited for?
    We don?t know yet. Because this is a relatively new approach, our understanding of where Ajax can best be applied is still in its infancy. Sometimes the traditional web application model is the most appropriate solution to a problem.
    Does this mean Adaptive Path is anti-Flash?
    Not at all. Macromedia is an Adaptive Path client, and we?ve long been supporters of Flash technology. As Ajax matures, we expect that sometimes Ajax will be the better solution to a particular problem, and sometimes Flash will be the better solution. We?re also interested in exploring ways the technologies can be mixed (as in the case of Flickr, which uses both).
    Where can I find examples of AJAX?
    While components of AJAX have been around for some time (for instance, 1999 for XMLHttpRequest), it really didn’t become that popular until Google took…
    What is the XMLHttpRequest object?
    It offers a non-blocking way for JavaScript to communicate back to the web server to update only part of the web page.
    Does Ajax have significant accessibility or browser compatibility limitations? Do Ajax applications break the back button? Is Ajax compatible with REST? Are there security considerations with Ajax development? Can Ajax applications be made to work for users who have JavaScript turned off?
    The answer to all of these questions is ?maybe?. Many developers are already working on ways to address these concerns. We think there?s more work to be done to determine all the limitations of Ajax, and we expect the Ajax development community to uncover more issues like these along the way.
    How do I access data from other domains to create a mashup with Java?
    From your JavaScript clients you can access data in other domains if the return data is provide in JSON format. In essence you can create a JavaScript client that runs operates using data from a different server. This technique is know as JSON with Padding or JSONP. There are questions as to whether this method is secure as you are retrieving data from outside your domain and allowing it to be excuted in the context of your domain. Not all data from third parties is accessible as JSON and in some cases you may want an extra level of protection. With Java you can provide a proxy to third party services using a web component such as a servlet. This proxy can manage the communication with a third party service and provide the data to your clients in a format of your choosing. You can also cache data at your proxy and reduce trips to service. For more on using a Java proxy to create mashups see The XmlHttpProxy Client for Java.
    Does Java have support for Comet style server-side push?
    Current AJAX applications use polling to communicate changes data between the server and client. Some applications, such as chat applications, stock tickers, or score boards require more immediate notifications of updates to the client. Comet is an event based low latency server side push for AJAX applications. Comet communication keeps one of the two connections available to the browser open to continously communicate events from the server to the client. A Java based solution for Comet is being developed for Glassfish on top of the Grizzly HTTP connector. See Enabling Grizzly by Jean-Francois Arcand for more details.
    How do I create a thread to do AJAX polling?
    JavaScript does not have threads. JavaScript functions are called when an event happens in a page such as the page is loaded, a mouse click, or a form element gains focus. You can create a timer using the setTimeout which takes a function name and time in milliseconds as arguments. You can then loop by calling the same function as can be seen in the JavaScript example below.
    function checkForMessage() {
    // start AJAX interaction with processCallback as the callback function
    }
    // callback for the request
    function processCallback() {
    // do post processing
    setTimeout(“checkForMessage()”, 10000);
    }
    Notice that the checkForMessage will continue to loop indefinitely. You may want to vary the increment the interval based on activity in the page or your use cases. You may also choose to have logic that would break out of the loop based on some AJAX response processing condition.
    Is the XMLHttpRequest object part of a W3C standard?
    No. Or not yet. It is part of the DOM Level 3 Load and Save Specification proposal.

    Categories
    LAMP MySQL PHP

    PHP common interview questions – answers

    =,==,=== – what is the difference between these?
    = assigns a value, == checks if value is the same, === checks if value is the same and the variables are of the exact same type.
    Echo, print, printf – what is the difference between these?
    Print and echo both output what is passed to them. Print acts like a function, so you can use it in complex statements. Printf is used to format the output.
    Include, include once, require – what is the difference between these?
    Include will includes a file each time it is called. Include_once would only include a file one time, so if a php program has a file in two include_once statements only the first will be done. Requre is like include, but if the file included is not available a fatal error occurs and processing stops.
    Are variables passed to functions by reference or value?
    A variable is passed by value unless the variable is passed with an &, such as functionName(&$variableName)
    How do you encrypt data?
    The PHP md5() function is very pretty widely used. The PHP crypt() function can also be used to encrypt data. (Honestly, the one time I had this question I drew a complete blank, so I’m not exactly certain what they were looking for.)
    What editor or ide do you use?
    Interesting question, probably does say something about your programming capabilites.  use Eclipse 3.1 with PHP extensions, , Zend Studio  Serious Unix users would be good with vi or emacs.
    PHP  Static, what are they and how do you use them?
    As with Java, if the job is for OO PHP (that is PHP 5), there will be a question on PHP static variables. You may be asked how to reference a static from inside and outside of the class it is in, or just show that you get the basic concept of a variable or function that is for the whole class and not an instance.
    Design Patterns general questions
    Now we are really into OO stuff. As in java job interviews I’ve usually been asked about design patterns in fairly vague terms, such as “describe the design patterns used in the systems you have worked on”. I was asked that so much that I drew out some UML to bring with me to interviews, as I found drawing up the UML during the interview to be distracting and slow.
    How can I maintain the count of how many persons have hit my site?
    The IP of a visitor can be tracked by
    $ip = $_SERVER[‘REMOTE_ADDR’];
    Just insert this value with date into a table.
    What is difference between mysql_fetch_array(), mysql_fetch_row() and mysql_fetch_object()?
    mysql_fetch_array()– Fetche resultset from a table in the form of array
    Eg: $res= mysql_query(’select * from tbl’)
    while ($row=mysql_fetch_array($res))
    mysql_fetch_row()
    Fetch single row
    mysql_fetch_object()
    Fetches resultset as object
    How I can make a chat page in php in simple
    On click on chat submit button store the values in the text area to a text file using PHP file functions.
    you can use ajax fore improved user experiance.
    wrie another javascript + ajax function to call the contents from the text file in each 3 sec


     
    What is the difference between echo and print statement?
    Print is a function and returns a value. Using echo we can use more than one parameter
    echo “and a “, 1, 2, 3; 
    What is differenc between mysql_connect and mysql_pconnect?
    mysql_connect- Creates a connection with db
    mysql_pconnect- creates a persistant connection with db 
    How I can get IP address of the user?
    )$ip = $_SERVER[‘REMOTE_ADDR’]; 
    How I will check that user is logged in or not?
    store user information in session

    I want to make it a function and I want to use it in each page and after login I want to go in current page?
    )store url in a variable and put in session before
    After login redirect page to that url 
    How do we know browser properties?
    var_dump($_SERVER); 
    If you have to work with dates in the following format: “Tuesday, February 14, 2006 @ 10:39 am”, how can you convert them to another format, that is easier to use?
    first remove @ from the string and than use strtime to convert this to unix time stamp.
    What is difference between require_once(), require(), include()?
    all are for including afile into another file
    require- if fails shoot a fatal error
    include- if fails shoot a warning
    include/require_once- for make sure that the page is included once in another page

    Categories
    PHP

    Difference between php4 & php5

    Differences between PHP4 and PHP5
    Here’s a quick overview of what has changed between PH4 and PHP5. PHP5 for the most part is backwards compatible with PHP4, but there are a couple key changes that might break your PHP4 script in a PHP5 environment. If you aren’t already, I stronly suggest you start developing for PHP5. Many hosts these days offer a PHP5 environment, or a dual PHP4/PHP5 setup so you should be fine on that end. Using all of these new features is worth even a moderate amount of trouble you might go through finding a new host!
    Note: Some of the features listed below are only in PHP5.2 and above.
    Object Model
    The new OOP features in PHP5 is probably the one thing that everyone knows for sure about. Out of all the new features, these are the ones that are talked about most!
    Passed by Reference
    This is an important change. In PHP4, everything was passed by value, including objects. This has changed in PHP5 — all objects are now passed by reference.
     

    PHP Code:
    $joe = new Person();
    $joe->sex 'male';  
    $betty $joe;
    $betty->sex 'female';
    echo $joe->sex// Will be 'female'  

    The above code fragment was common in PHP4. If you needed to duplicate an object, you simply copied it by assigning it to another variable. But in PHP5 you must use the new clone keyword.
     
    Note that this also means you can stop using the reference operator (&). It was common practice to pass your objects around using the & operator to get around the annoying pass-by-value functionality in PHP4.
    Class Constants and Static Methods/Properties
    You can now create class constants that act much the same was as define()’ed constants, but are contained within a class definition and accessed with the :: operator.
    Static methods and properties are also available. When you declare a class member as static, then it makes that member accessible (through the :: operator) without an instance. (Note this means within methods, the $this variable is not available)
    Visibility
    Class methods and properties now have visibility. PHP has 3 levels of visibility:

    1. Public is the most visible, making methods accessible to everyone and properties readable and writable by everyone.
    2. Protected makes members accessible to the class itself and any subclasses as well as any parent classes.
    3. Private makes members only available to the class itself.

    Unified Constructors and Destructors
    PHP5 introduces a new unified constructor/destructor names. In PHP4, a constructor was simply a method that had the same name as the class itself. This caused some headaches since if you changed the name of the class, you would have to go through and change every occurrence of that name.
    In PHP5, all constructors are named __construct(). That is, the word construct prefixed by two underscores. Other then this name change, a constructor works the same way.
    Also, the newly added __destruct() (destruct prefixed by two underscores) allows you to write code that will be executed when the object is destroyed.
    Abstract Classes
    PHP5 lets you declare a class as abstract. An abstract class cannot itself be instantiated, it is purely used to define a model where other classes extend. You must declare a class abstract if it contains any abstract methods. Any methods marked as abstract must be defined within any classes that extend the class. Note that you can also include full method definitions within an abstract class along with any abstract methods.
    Interfaces
    PHP5 introduces interfaces to help you design common APIs. An interface defines the methods a class must implement. Note that all the methods defined in an interface must be public. An interface is not designed as a blueprint for classes, but just a way to standardize a common API.
    The one big advantage to using interfaces is that a class can implement any number of them. You can still only extend on parent class, but you can implement an unlimited number of interfaces.
    Magic Methods
    There are a number of “magic methods” that add an assortment to functionality to your classes. Note that PHP reserves the naming of methods prefixed with a double-underscore. Never name any of your methods with this naming scheme!
    Some magic methods to take note of are __call, __get, __set and __toString. These are the ones I find most useful.
    Finality
    You can now use the final keyword to indicate that a method cannot be overridden by a child. You can also declare an entire class as final which prevents it from having any children at all.
    The __autoload Function
    Using a specially named function, __autoload (there’s that double-underscore again!), you can automatically load object files when PHP encounters a class that hasn’t been defined yet. Instead of large chunks of include’s at the top of your scripts, you can define a simple autoload function to include them automatically.

    PHP Code:
    function __autoload($class_name) {
         require_once 
    "./includes/classes/$class_name.inc.php";
    }  

    Note you can change the autoload function or even add multiple autoload functions using spl_autoload_register and related functions.
     
    Standard PHP Library
    PHP now includes a bunch of functionality to solve common problems in the so-named SPL. There’s a lot of cool stuff in there, check it out!
    For example, we can finally create classes that can be accessed like arrays by implementing the ArrayAccess interface. If we implement the Iterator interface, we can even let our classes work in situations like the foreach construct.
    Miscellaneous Features
    Type Hinting
    PHP5 introduces limited type hinting. This means you can enforce what kind of variables are passed to functions or class methods. The drawback is that (at this time), it will only work for classes or arrays — so no other scalar types like integers or strings.
    To add a type hint to a parameter, you specify the name of the class before the $. Beware that when you specify a class name, the type will be satisfied with all of its subclasses as well.

    PHP Code:
    function echo_user(User $user) {
        echo 
    $user->getUsername();
    }  

    If the passed parameter is not User (or a subclass of User), then PHP will throw a fatal error.
    Exceptions
    PHP finally introduces exceptions! An exception is basically an error. By using an exception however, you gain more control the simple trigger_error notices we were stuck with before.
    An exception is just an object. When an error occurs, you throw an exception. When an exception is thrown, the rest of the PHP code following will not be executed. When you are about to perform something “risky”, surround your code with atry block. If an exception is thrown, then your following catch block is there to intercept the error and handle it accordingly. If there is no catch block, a fatal error occurs.

    PHP Code:
    try {
        
    $cache->write();
    } catch (
    AccessDeniedException $e) {
        die(
    'Could not write the cache, access denied.');
    } catch (
    Exception $e) {
       die(
    'An unknown error occurred: ' $e->getMessage());
    }  

    E_STRICT Error Level
    There is a new error level defined as E_STRICT (value 2048). It is not included in E_ALL, if you wish to use this new level you must specify it explicitly. E_STRICT will notify you when you use depreciated code. I suggest you enable this level so you can always stay on top of things.
    Foreach Construct and By-Reference Value
    The foreach construct now lets you define the ‘value’ as a reference instead of a copy. Though I would suggest againstusing this feature, as it can cause some problems if you aren’t careful:

    PHP Code:
    foreach($array as $k => &$v) {
        
    // Nice and easy, no working with $array[$k] anymore
        
    $v htmlentities($v);
    }  
    // But be careful, this will have an unexpected result because
    // $v will still be a reference to the last element of the $array array
    foreach($another_array as $k => $v) {
    }  



    New Functions
    PHP5 introduces a slew of new functions. You can get a list of them from the PHP Manual.
    New Extensions
    PHP5 also introduces new default extensions.

    • SimpleXML for easy processing of XML data
    • DOM and XSL extensions are available for a much improved XML-consuming experience. A breath of fresh air after using DOMXML for PHP4!
    • PDO for working with databases. An excellent OO interface for interacting with your database.
    • Hash gives you access to a ton of hash functions if you need more then the usual md5 or sha1.

    Compatibility Issues
    The PHP manual has a list of changes that will affect backwards compatibility. You should definately read through that page, but here is are three issues I have found particularly tiresome:

    • array_merge() will now give you warnings if any of the parameters are not arrays. In PHP4, you could get away with merging non-arrays with arrays (and the items would just be added if they were say, a string). Of course it was bad practice to do this to being with, but it can cause headaches if you don’t know about it.
    • As discussed above, objects are now passed by references. If you want to copy a object, make sure to use theclone keyword.
    • get_*() now return names as they were defined. If a class was called MyTestClass, then get_class() will return that — case sensitive! In PHP4, they were always returned in lowercase.
    Categories
    MySQL PHP

    Freshers PHP/MySQL Technical Interview Questions & Answers

    Freshers PHP Technical Interview Questions & Answers


    Question : What are the differences between Get and post methods in form submitting. Give the case where we can use get and we can use post methods?
    Answer : When to use GET or POST

    The HTML 2.0 specification says, in section Form Submission (and the HTML 4.0 specification repeats this with minor stylistic changes):

    –>If the processing of a form is idempotent (i.e. it has no lasting observable effect on the state of the
    world), then the form method should be GET. Many database searches have no visible side-effects and make ideal applications of query forms.

    –>If the service associated with the processing of a form has side effects (for example, modification of a database or subscription to a service), the method should be POST.

    How the form data is transmitted?

    quotation from the HTML 4.0 specification

    –> If the method is “get” – -, the user agent takes the value of action, appends a ? to it, then appends the form data set, encoded using the application/x-www-form-urlencoded content type. The user agent then traverses the link to this URI. In this scenario, form data are restricted to ASCII codes.
    –> If the method is “post” –, the user agent conducts an HTTP post transaction using the value of the action attribute and a message created according to the content type specified by the enctype
    attribute.

    Quote from CGI FAQ

    Firstly, the the HTTP protocol specifies differing usages for the two methods. GET requests should always be idempotent on the server. This means that whereas one GET request might (rarely) change some state on the Server, two or more identical requests will have no further effect.

    This is a theoretical point which is also good advice in practice. If a user hits “reload” on his/her browser, an identical request will be sent to the server, potentially resulting in two identical database or guestbook entries, counter increments, etc. Browsers may reload a GET URL automatically, particularly if cacheing is disabled (as is usually the case with CGI output), but will typically prompt the user before re-submitting a POST request. This means you’re far less likely to get inadvertently-repeated entries from POST.

    GET is (in theory) the preferred method for idempotent operations, such as querying a database, though it matters little if you’re using a form. There is a further practical constraint that many systems have built-in limits to the length of a GET request they can handle: when the total size of a request (URL+params) approaches or exceeds 1Kb, you are well-advised to use POST in any
    case.

    I would prefer POST when I don’t want the status to be change when user resubmits. And GET
    when it does not matter.

    Question : Who is the father of PHP and explain the changes in PHP versions?

    Answer : Rasmus Lerdorf is known as the father of PHP.PHP/FI 2.0 is an early and no longer supported version of PHP. PHP 3 is the successor to PHP/FI 2.0 and is a lot nicer. PHP 4 is the current generation of PHP, which uses the Zend engine under the hood. PHP 5 uses Zend engine 2 which, among other things, offers many additional OOPs features.

    Question : How can we submit a form without a submit button?

    Answer : The main idea behind this is to use Java script submit() function in order to submit the form without explicitly clicking any submit button. You can attach the document.formname.submit() method to onclick, onchange events of different inputs and perform the form submission. you
    can even built a timer function where you can automatically submit the form after xx seconds once the loading is done (can be seen in online test sites).

    Question : In how many ways we can retrieve the data in the result set of
    MySQL using PHP?

    Answer : You can do it by 4 Ways

    1. mysql_fetch_row.
    2. mysql_fetch_array
    3. mysql_fetch_object
    4. mysql_fetch_assoc

    Question : What is the difference between mysql_fetch_object and
    mysql_fetch_array?

    Answer : mysql_fetch_object() is similar to mysql_fetch_array(), with one difference –
    an object is returned, instead of an array. Indirectly, that means that you can only access the data by the field names, and not by their offsets (numbers are illegal property names).

    Question : What is the difference between $message and $$message?

    Answer : It is a classic example of PHP’s variable variables. take the following example.

    $message = “Raghav”;

    $$message = “is a owner of http://localhost/wordpress/ “;

    $message is a simple PHP variable that we are used to. But the $$message is not a very familiar face. It creates a variable name $mizan with the value “is a moderator of PHPXperts.” assigned. break it like this${$message} => $mizanSometimes it is convenient to be able to have variable variable names. That is, a variable name which can be set and used dynamically.

    Question : How can we extract string ‘hotmail.com ‘ from a string raghav.cool@hotmail.com using regular expression of PHP?

    Answer : preg_match(”/^http://.+@(.+)$/”,’raghav.cool@hotmail.com’,$found);
    echo $found[1];

    Question : How can we create a database using PHP and MySQL?

    Answer : We can create MySQL Database with the use of mysql_create_db(“Database Name”).

    Question : What are the differences between require and include, include_once and require_once?

    Answer :

    The include() statement includes and evaluates the specified file.The documentation below also applies to require(). The two constructs are identical in every way except how they handle
    failure. include() produces a Warning while require() results in a Fatal Error. In other words, use
    require() if you want a missing file to halt processing of the page. include() does not behave this way, the script will continue regardless. The include_once() statement includes and evaluates the
    specified file during the execution of the script. This is a behavior similar to the include() statement, with the only difference being that if the code from a file has already been included, it will not be
    included again. As the name suggests, it will be included just once.include_once() should be used in cases where the same file might be included and evaluated more than once during a particular execution of a script, and you want to be sure that it is included exactly once to avoid problems with function redefinitions, variable value reassignments, etc. require_once() should be used in cases where the same file might be included and evaluated more than once during a particular execution of a script, and you want to be sure that it is included exactly once to avoid problems with function
    redefinitions, variable value reassignments, etc.

    Question : Can we use include (”abc.PHP”) two times in a PHP page “makeit.PHP”?

    Answer : Yes we can use include() more than one time in any page though it is not a very good practice.

    Question : What are the different tables present in MySQL, which type of table is generated when we are creating a table in the following syntax:
    create table employee (eno int(2),ename varchar(10)) ?

    Answer : Total 5 types of tables we can create
    1. MyISAM
    2. Heap
    3. Merge
    4. INNO DB
    5. ISAM
    MyISAM is the default storage engine as of MySQL 3.23 and as a result if
    we do not specify the table name explicitly it will be assigned to the
    default engine.

    Question : Functions in IMAP, POP3 AND LDAP?

    Answer : You can find these specific information in PHP Manual.

    Question : How can I execute a PHP script using command line?

    Answer : As of version 4.3.0, PHP supports a new SAPI type (Server Application Programming Interface) named CLI which means Command Line Interface. Just run the PHP CLI (Command Line Interface) program and provide the PHP script file name as the command line argument. For example, “php myScript.php”, assuming “php” is the command to invoke the CLI program.
    Be aware that if your PHP script was written for the Web CGI interface, it may not execute properly in command line environment.

    Question : Suppose your Zend engine supports the mode <? ?>. Then how can you
    configure your PHP Zend engine to support <?php ?>mode ?

    Answer : In php.ini file:
    set
    short_open_tag=on
    to make PHP support

    Question : Shopping cart online validation i.e. how can we configure Paypal,
    etc.?

    Answer : We can find the detail documentation about different paypal integration process at the following site PayPal PHP
    SDK : http://www.paypaldev.org/

    Question : What is meant by nl2br()?

    Answer : Inserts HTML line breaks
    (
    )
    before all newlines in a string string nl2br (string); Returns string with ” inserted before all newlines.
    For example: echo nl2br(”god bless/n you”) will output “god bless
    you” to your browser.

    Question : Draw the architecture of Zend engine?

    Answer : The Zend Engine is the internal compiler and runtime engine used by PHP4. Developed by Zeev Suraski and Andi Gutmans, the Zend Engine is an
    abbreviation of their names. In the early days of PHP4, it worked as follows:

    The PHP script was loaded by the Zend Engine and compiled into Zend opcode. Opcodes, short for operation codes, are low level binary instructions. Then the opcode was executed and the HTML generated sent to the client. The opcode was flushed from memory after execution.Today, there are a multitude of products and techniques to help you speed up this process. In the following diagram, we show the how modern PHP scripts work; all the shaded boxes are optional.

    PHP Scripts are loaded into memory and compiled into Zend opcodes.

    Question : What are the current versions of apache, PHP, and MySQL?

    Answer : As of Aug 2008 the current versions are PHP: php5.2.6
    MySQL: MySQL 5.1.2
    Apache: Apache 2.2.9
    Note: visit
    http://www.php.net/,
    http://dev.mysql.com/downloads/mysql/,
    http://www.apache.org/ to get current
    versions.

    Question : What are the reasons for selecting lamp (Linux, apache, MySQL,
    PHP) instead of combination of other software programs, servers and operating systems?

    Answer : All of those are open source resource. Security of Linux is very very more than windows. Apache is a better server that IIS both in functionality and security. MySQL is world most popular open source database. PHP is more faster that asp or any other scripting language.

    Question : How can we encrypt and decrypt a data present in a MySQL table using MySQL?

    Answer : AES_ENCRYPT () and AES_DECRYPT ()

    Question : How can we encrypt the username and password using PHP?

    Answer : The functions in this section perform encryption and decryption, and
    compression and uncompression:

    Encryption Decryption
    AES_ENCRYT() AES_DECRYPT()
    ENCODE() DECODE()
    DES_ENCRYPT() DES_DECRYPT()
    ENCRYPT() Not available
    MD5() Not available
    OLD_PASSWORD() Not available
    PASSWORD() Not available
    SHA() or SHA1() Not available
    Not available UNCOMPRESSED_LENGTH()

    Question : What are the features and advantages of object-oriented programming?

    Answer : One of the main advantages of OO programming is its ease of modification; objects can easily be modified and added to a system there by reducing maintenance costs. OO programming is also considered to be better at modeling the real world than is procedural programming. It allows for more complicated and flexible interactions. OO systems are also easier for non-technical personnel to understand and easier for them to participate in the maintenance and enhancement of a system because it appeals to natural human cognition patterns. For some systems, an OO approach can speed development time since many objects are standard across systems and can be reused. Components that manage dates, shipping, shopping carts, etc. can be purchased and easily modified for a specific system.

    Question : What are the differences between procedure-oriented languages and
    object-oriented languages?

    Answer : Traditional programming has the following characteristics:Functions are written sequentially, so that a change in programming can affect any code that follows it. If a function is used multiple times in a system (i.e., a piece of code that manages the date), it is often simply cut and pasted into each program (i.e., a change log, order function, fulfillment system, etc). If a date change is needed (i.e., Y2K when the code needed to be changed to handle four numerical digits instead of two), all these pieces of code must be found, modified, and tested. Code (sequences of computer instructions) and data (information on which the instructions operates on) are kept separate. Multiple sets of code can access and modify one set of data. One set of code may rely on data in multiple places. Multiple sets of code and data are required to work together. Changes made to any of the code sets and data sets can cause problems through out the system.Object-Oriented programming takes a radically different approach:Code and data are merged into one indivisible item – an object (the term “component” has also been used to describe an object.) An object is an abstraction of a set of real-world things (for example, an object may be created around “date”) The object would contain all information and
    functionality for that thing (A date object it may contain labels like January, February, Tuesday, Wednesday.
    It may contain functionality that manages leap years, determines if it is a business day or a holiday, etc., See Fig. 1). Ideally, information about a particular thing should reside in only one place in a system.The information within an object is encapsulated (or hidden) from the rest of the system. A system is composed of multiple objects (i.e., date function, reports, order processing, etc., See Fig 2). When one object needs information from another object, a request is sent asking for specific information. (for example, a report object may need to know what today’s date is and will send a request to the date object) These requests are called messages and each object has an interface that manages messages. OO programming languages include features such as “class”, “instance”, “inheritance”, and “polymorphism” that increase the power and
    flexibility of an object.

    Question : What is the use of friend function?

    Answer : Sometimes a function is best shared among a number of different classes. Such functions can be declared either as member functions of one class or as global functions. In either case they can be set to be friends of other classes, by using a friend specifier in the class that is admitting them. Such functions can use all attributes of the class which names them as a friend, as if they were themselves members of that class. A friend declaration is essentially a prototype for a member function, but instead of requiring an implementation with the name of that class attached by the double colon syntax, a global function or member function of another class provides the match.

    Question : What are the differences between public, private, protected,static, transient, final and volatile?

    Answer : Public: Public declared items can be accessed everywhere.
    Protected: Protected limits access to inherited and parent classes (and to the class that defines the item).
    Private: Private limits visibility only to the class that defines the item.
    Static: A static variable exists only in a local function scope, but it does not lose its value when program execution leaves this scope.
    Final: Final keyword prevents child classes from overriding a method by prefixing the definition with final. If the class itself is being defined final then it cannot be extended.
    Transient: A transient variable is a variable that may not be serialized.
    Volatile: a variable that might be concurrently modified by multiple threads should be declared volatile. Variables declared to be volatile will not be optimized by the compiler because their value can change at any time.

    Question : What are the different types of errors in PHP?

    Answer : Three are three types of errors:1. Notices: These are trivial, non-critical errors that PHP encounters while executing a script – for example, accessing a variable that has not yet been defined. By default, such errors are not displayed to the user at all – although, as you will see, you can change this default behavior.2. Warnings: These are more serious errors – for example, attempting to include() a file which does not exist. By default, these errors are displayed to the user, but they do not result in script termination.3. Fatal errors: These are critical errors – for example,
    instantiating an object of a non-existent class, or calling a non-existent function. These errors cause the immediate termination of the script, and PHP’s default behavior is to display them to the user when they take place.

    Question : What is the functionality of the function strstr and stristr?

    Answer : strstr:
    Returns part of haystack string from the first occurrence of needle to the end of haystack.If needle is not found, returns FALSE. If needle is not a string, it is converted to an integer and applied as the ordinal value of a character. This function is case-sensitive. For case-insensitive searches, use stristr().

    Question : What are the differences between PHP 3 and PHP 4 and PHP 5?

    Answer : PHP 3 is most procedure oriented and , PHP4 and PHP5 aer object oriented. For more details
    http://php.net/

    Question : How can we convert asp pages to PHP pages?

    Answer : There are lots of tools available for asp to PHP conversion. you can search Google for that. the best one is available at http://asp2php.naken.cc/

    Question : What is the functionality of the function htmlentities?

    Answer : Convert all applicable characters to HTML entities
    This function is identical to htmlspecialchars() in all ways, except with htmlentities(), all characters which have HTML character entity equivalents are translated into these entities.

    Question : How can we get second of the current time using date function?

    Answer : $second = date(”s”);

    Question : How can we convert the time zones using PHP?

    Answer : By using date_default_timezone_get and
    date_default_timezone_set function on PHP 5.1.0
    <!–p// Discover what 8am in Tokyo relates to on the East Coast of the US
    // Set the default timezone to Tokyo time:
    date_default_timezone_set(’Asia/Tokyo’);
    // Now generate the timestamp for that particular timezone, on Jan 1st, 2000
    $stamp = mktime(8, 0, 0, 1, 1, 2000);
    // Now set the timezone back to US/Eastern
    date_default_timezone_set(’US/Eastern’);
    // Output the date in a standard format (RFC1123), this will  print:
    // Fri, 31 Dec 1999 18:00:00 EST
    echo ‘
    ‘, date(DATE_RFC1123, $stamp) ,’
    ‘; ?>

    Question : What is meant by urlencode and urldecode?

    Answer : URLencode returns a string in which all non-alphanumeric characters except -_. have been replaced with a percent (%) sign followed by two hex digits and spaces encoded as plus (+) signs. It is encoded the same way that the posted data from a WWW form
    is encoded, that is the same way as in application/x-www-form-urlencoded media type. urldecode decodes any %## encoding in the given string.

    Question : What is the difference between the functions unlink and unset?

    Answer : unlink() deletes the given file from the file system.
    unset() makes a variable undefined.

    Question : How can we register the variables into a session?

    Answer : $_SESSION[’name’] = “RAGHAV”;

    Question : How can we get the properties (size, type, width, height) of an image using PHP image functions?

    Answer : To know the Image type use exif_imagetype () function
    To know the Image size use getimagesize () function
    To know the image width use imagesx () function
    To know the image height use imagesy() function

    Question : How can we get the browser properties using PHP?

    Answer : By using
    $_SERVER[’HTTP_USER_AGENT’] variable.

    Question : What is the maximum size of a file that can be uploaded using PHP
    and how can we change this?

    Answer : By default the maximum size is 2MB. and we can change the following setup at php.iniupload_max_filesize = 2M

    Question : How can we increase the execution time of a PHP script?

    Answer : by changing the following setup at php.inimax_execution_time = 30; Maximum execution time of each script, in seconds

    Question : How can we take a backup of a MySQL table and how can we restore it. ?

    Answer : To backup: BACKUP TABLE tbl_name[,tbl_name…] TO ‘/path/to/backup/directory’
    RESTORE TABLE tbl_name[,tbl_name…] FROM ‘/path/to/backup/directory’mysqldump: Dumping Table Structure and DataUtility to dump a database or a collection of database for backup or for transferring the data to another SQL server (not necessarily a MySQL server). The dump will contain SQL statements to create the table and/or populate the table. -t, –no-create-info Don’t write table creation information (the CREATE TABLE statement). -d, –no-data Don’t write any row information for the table. This is very useful if you just want to get a dump of the structure for a table!

    Question : How can we optimize or increase the speed of a MySQL select query?

    Answer : • First of all instead of using select * from table1, use select column1, column2, column3.. from table1
    •Look for the opportunity to introduce index in the table you are  querying.
    •use limit keyword if you are looking for any specific number of rows from the result set.

    Question : How many ways can we get the value of current session id?

    Answer : session_id() returns the session id for the current session.

    Question : How can we destroy the session, how can we unset the variable of a session?

    Answer : session_unregister — Unregister a global variable from the current session

    session_unset — Free all session variables

    Question : How can we destroy the cookie?

    Answer : Set the cookie in past.

    Question : How many ways we can pass the variable through the navigation between the pages?

    Answer : •GET/QueryString
    •POST

    Question : What is the difference between ereg_replace() and eregi_replace()?

    Answer : eregi_replace() function is identical to ereg_replace() except that this ignores case distinction when matching alphabetic characters.eregi_replace() function is identical to ereg_replace() except that this ignores case distinction when matching alphabetic characters.

    Question : What are the different functions in sorting an array?

    Answer : Sort(), arsort(),
    asort(), ksort(),
    natsort(), natcasesort(),
    rsort(), usort(),
    array_multisort(), and
    uksort().

    Question : How can we know the count/number of elements of an array?

    Answer : 2 ways
    a) sizeof($urarray) This function is an alias of count()
    b) count($urarray)

    Question : What is the PHP predefined variable that tells the What types of
    images that PHP supports?

    Answer : Though i am not sure if this is wrong or not, With the exif extension you are able to work with image meta data.

    Question : How can I know that a variable is a number or not using a JavaScript?

    Answer : bool is_numeric ( mixed var) Returns TRUE if var is a number or a numeric string, FALSE otherwise.or use isNaN(mixed var)The isNaN() function is used to check if a value is not a number.

    Question : List out some tools through which we can draw E-R diagrams for mysql.

    Answer :
    Case Studio
    Smart Draw

    Question : How can I retrieve values from one database server and store themin other database server using PHP?

    Answer : WeWe can always fetch from one database and rewrite to another. Here is a nice solution of it.
    $db1 = mysql_connect(”host”,”user”,”pwd”);
    mysql_select_db(”db1?, $db1);
    $res1 = mysql_query(”query”,$db1);
    $db2 = mysql_connect(”host”,”user”,”pwd”);
    mysql_select_db(”db2?, $db2);
    $res2 = mysql_query(”query”,$db2);
    At this point you can only fetch records from you previous ResultSet, i.e $res1 – But you cannot execute new query in $db1, even if yousupply the link as because the link was overwritten by the new db.so at this point the following script will fail
    $res3 = mysql_query(”query”,$db1); //this will failSo how to solve that? take a look below.
    $db1 = mysql_connect(”host”,”user”,”pwd”);
    mysql_select_db(”db1?, $db1);
    $res1 = mysql_query(”query”,$db1);
    $db2 = mysql_connect(”host”,”user”,”pwd”, true);
    mysql_select_db(”db2?, $db2);
    $res2 = mysql_query(”query”,$db2);
    So mysql_connect has another optional boolean parameter whichindicates whether a link will be created or not. As we connect to the $db2 with this optional parameter set to ‘true’, so both link willremain live. Now the following query will execute successfully.
    $res3 = mysql_query(”query”,$db1);

    Question : List out the predefined classes in PHP?

    Answer : Directory
    stdClass
    __PHP_Incomplete_Class
    exception
    php_user_filter

    Question : How can I make a script that can be bi-language (supports  English, German)?

    Answer : You can maintain two separate language file for each of the language. All the labels are putted in both language files as variables and assign those variables in the PHP source. On run-time choose the required language option.

    Question : What are the difference between abstract class and interface?

    Answer : Abstract class: abstract classes are the class where one or moremethods are abstract but not necessarily all method has to be abstract.

    Abstract methods are the methods, which are declare in its class but not defined. The definition of those methods must be in its extending class.

    Interface: Interfaces are one type of class where all the methods are abstract. That means all the methods only declared but not defined. All the methods must be defined by its implemented class.

    Question : How can we send mail using JavaScript?

    Answer : JavaScript does not have any networking capabilities as it isdesigned to work on client site. As a result we can not send mails usingJavaScript. But we can call the client side mail protocol mailtovia JavaScript to prompt for an Email  to send. this requires the client to approve it.

    Question : How can we repair a MySQL table?

    Answer : The syntex for repairing a MySQL table is REPAIR TABLENAME, [TABLENAME, ], [Quick],[Extended].This command will repair the table specified if the quick is given the MySQL will do a repair of only the index tree if the extended is givenit will create index row by row.

    Question : What are the advantages of stored procedures, triggers, indexes?

    Answer : A stored procedure is a set of SQL commands that can be compiled andstored in the server. Once this has been done, clients don’t need tokeep re-issuing the entire query but can refer to the stored procedure.This provides better overall performance because the query has to beparsed only once, and less information needs to be sent between theserver and the client. You can also raise the conceptual level by havinglibraries of functions in the server. However, stored procedures ofcourse do increase the load on the database server system, as more of the work is done on the server side and less on the client (application)side.Triggers will also be implemented. A trigger is effectively a type of stored procedure, one that is invoked when a particular event occurs.For example, you can install a stored procedure that is triggered each time a record is deleted from a transaction table and that stored procedure automatically deletes the corresponding customer from a customer table when all his transactions are deleted.Indexes are used to find rows with specific column values quickly.Without an index, MySQL must begin with the first row and then read through the entire table to find the relevant rows. The larger the table, the more this costs. If the table has an index for the columns in question, MySQL can quickly determine the position to seek to in the middle of the data file without having to look at all the data. If a table has 1,000 rows, this is at least 100 times faster than reading sequentially. If you need to access most of the rows, it is faster to read sequentially, because this minimizes disk seeks.

    Question : What is the maximum length of a table name, database name and field name in MySQL?

    Answer : The following table describes the maximum length for each type of identifier.

    Identifier Maximum Length(bytes)
    Database 64
    Table 64
    Column 64
    Index 64
    Alias 255

    There are some restrictions on the characters that may appear in identifiers.

    Question : How many values can the SET function of MySQL take?

    Answer : MySQL set can take zero or more values but at the maximum it can take 64 values.

    Question : What are the other commands to know the structure of table using MySQL commands except explain command?

    Answer : describe Table-Name;

    Question : How many tables will create when we create table, what are they?

    Answer : The ‘.frm’ file stores the table definition.The data file has a ‘.MYD’ (MYData) extension.The index file has a ‘.MYI’ (MYIndex) extension.

    Question : What is the purpose of the following files having extensions 1) .frm2) .myd 3) .myi? What do these files contain?

    Answer : In MySql, the default table type is MyISAM.Each MyISAM table is stored on disk in three files. The files have names that begin with the table name and have an extension to indicate the file type.The ‘.frm’ file stores the table definition.The data file has a ‘.MYD’ (MYData) extension.The index file has a ‘.MYI’ (MYIndex) extension.

    Question : What is maximum size of a database in MySQL?

    Answer : If the operating system or file system places a limit on the number of files in a directory, MySQL is bound by that constraint.The efficiency of the operating system in handling large numbers offiles in a directory can place a practical limit on the number of tables in a database. If the time required to open a file in the directory increases significantly as the number of files increases, database performance can be adversely affected.The amount of available disk space limits the number of tables.MySQL 3.22 had a 4GB (4 gigabyte) limit on table size. With the MyISAM storage engine in MySQL 3.23, the maximum table size was increased to65536 terabytes (2567 – 1 bytes). With this larger allowed table size,the maximum effective table size for MySQL databases is usually determined by operating system constraints on file sizes, not by MySQL internal limits.The InnoDB storage engine maintains InnoDB tables within a table space that can be created from several files. This allows a table to exceed the maximum individual file size. The table space can include raw disk partitions, which allows extremely large tables. The maximum table space size is 64TB.The following table lists some examples of operating system file-size limits. This is only a rough guide and is not intended to be definitive.For the most up-to-date information, be sure to check the documentationspecific to your operating system.Operating System File-size Limit Linux 2.2-Intel 32-bit 2GB (LFS: 4GB)
    Linux 2.4+ (using ext3 filesystem) 4TB
    Solaris 9/10 16TB
    NetWare w/NSS filesystem 8TB
    Win32 w/ FAT/FAT32 2GB/4GB
    Win32 w/ NTFS 2TB (possibly larger)
    MacOS X w/ HFS+ 2TB

    Question : Give the syntax of Grant and Revoke commands?

    Answer : The generic syntax for grant is as following :
    > GRANT [rights] on [database/s] TO [username@hostname] IDENTIFIED BY[password]now rights can be a) All privileges b) combination of create, drop, select, insert, update and delete etc. We can grant rights on all databse by using *.* or some specificdatabase by database.* or a specific table by database.table_name username@hotsname can be either username@localhost, username@hostname and username@% where hostname is any valid hostname and % represents any name, the *.*any condition password is simply the password of user.
    The generic syntax for revoke is as following :
    > REVOKE [rights] on [database/s] FROM [username@hostname] now rights can be as explained above a) All privileges b) combination of create, drop, select, insert, update and delete etc.username@hotsname can be either username@localhost, username@hostname and username@% where hostname is any valid hostname and % represents any name, the *.*any condition

    Question : Explain Normalization concept?

    Answer : The normalization process involves getting our data to conform to three progressive normal forms, and a higher level of normalization cannot be achieved until the previous levels have been achieved (there are actually five normal forms, but the last two are mainly academic and will not be discussed).First Normal Form  The First Normal Form (or 1NF) involves removal of redundant data from horizontal rows. We want to ensure that there is no duplication of data in a given row, and that every column stores the least amount of information possible (making the field atomic). Second Normal Form Where the First Normal Form deals with redundancy of data across a horizontal row, Second Normal Form (or 2NF) deals with redundancy of data in vertical columns. As stated earlier, the normal forms are progressive, so to achieve Second Normal Form, your tables must already be in First Normal Form.Third Normal Form I have a confession to make; I do not often use Third Normal Form. In Third Normal Form we are looking for data in our tables that is not fully dependent on the primary key, but dependent on another value in the table.

    Question : How can we find the number of rows in a table using MySQL?

    Answer : Use this for mysql>SELECT COUNT(*) FROM table_name;

    Question : How can we find the number of rows in a result set using PHP?

    Answer :
    $result = mysql_query($sql, $db_link);
    $num_rows = mysql_num_rows($result);
    echo “$num_rows rows found”;

    Question : How many ways we can we find the current date using MySQL?

    Answer :
    SELECT CURDATE();
    CURRENT_DATE() = CURDATE()
    for time use SELECT CURTIME();
    CURRENT_TIME() = CURTIME()

    Question : What are the advantages and disadvantages of Cascading Style Sheets?

    Answer :
    External Style Sheets
    Advantages : Can control styles for multiple documents at once. Classes can be created for use on multiple HTML element types in many documents.Selector and grouping methods can be used to apply styles under complex contexts.
    Disadvantages : An extra download is required to import style information for eachdocument The rendering of the document may be delayed until the externalstyle sheet is loaded becomes slightly unwieldy for small quantities ofstyle definitions.
    Embedded Style Sheets
    Advantages : Classes can be created for use on multiple tag types in the document.Selector and grouping methods can be used to apply styles under complexcontexts. No additional downloads necessary to receive style information.
    Disadvantages : This method can not control styles for multiple documents at once.
    Inline Styles
    Advantages : Useful for small quantities of style definitions. Can override otherstyle specification methods at the local level so only exceptions needto be listed in conjunction with other style methods.
    Disadvantages : Does not distance style information from content (a main goal ofSGML/HTML). Can not control styles for multiple documents at once.Author can not create or control classes of elements to control multipleelement types within the document. Selector grouping methods can not beused to create complex element addressing scenarios

    Question : What type of inheritance that PHP supports?

    Answer : In PHP an extended class is always dependent on a single base class,that is, multiple inheritance is supported by interfaces. Classes are extended using the keyword ‘extends’.

    Question : What is the difference between Primary Key and Unique key?

    Answer : Primary Key: A column in a table whose values uniquely identify therows in the table. A primary key value cannot be NULL. Unique Key: Unique Keys are used to uniquely identify each row in thetable. There can be one and only one row for each unique key value. So NULL can be a unique key.There can be only one primary key for a table but there can be morethan one unique for a table.

    Question : The structure of table view buyers is as follows:

    Field Type Null Key Default Extra
    user_pri_id int(15) PRI null auto_increment
    userid varchar(10) YES null

    the value of user_pri_id the last row 999 then What will happen inthe following conditions?Condition1: Delete all the rows and insert another row then.What is the starting value for this auto incremented field user_pri_id ,Condition2: Delete the last row(having the field value 999) andinsert another row then. What is the value for this auto incremented field user_pri_id.

    Answer : In both cases let the value for auto increment field be n then nextrow will have value n+1 i.e. 1000.

    Question : What are the advantages/disadvantages of MySQL and PHP?

    Answer : Both of them are open source software (so free of cost), supportcross platform. php is faster then ASP and JSP.

    Question : What is the difference between GROUP BY and ORDER BY in Sql?

    Answer : ORDER BY [col1],[col2],…,[coln]; Tells DBMS according to what columns it should sort the result. If two rows will have the same value in col1it will try to sort them according to col2 and so on.GROUP BY[col1],[col2],…,[coln]; Tells DBMS to group results with same value of column col1. You can use COUNT(col1), SUM(col1), AVG(col1) with it, if you want to count all items in group, sum all values or view average.

    Question : What is the difference between char and varchar data types?

    Answer : Set char to occupy n bytes and it will take n bytes even if u r storing a value of n-m bytes Set varchar to occupy n bytes and it will take only the required space and will not use the n bytes eg. name char(15) will waste 10 bytes if we store ‘mizan’, if each char takes a byte eg. name varchar(15) will just use 5 bytes if we store ‘mizan’, if each char takes a byte. rest 10 bytes will be free.

    Question : What is the functionality of md5 function in PHP?

    Answer : Calculate the md5 hash of a string. The hash is a 32-characterhexadecimal number. I use it to generate keys which I use to identifyusers etc. If I add random no techniques to it the md5 generated nowwill be totally different for the same string I am using.

    Question : How can I load data from a text file into a table?

    Answer : you can use LOAD DATA INFILE file_name; syntax to load datafrom a text file. but you have to make sure thata) data is delimitedb) columns and data matched correctly.

    Question : How can we know the number of days between two given dates using MySQL?

    Answer : SELECT DATEDIFF(’2007-03-07?,’2005-01-01?);

    Question : How can we know the number of days between two given dates using PHP?

    Answer : $date1 = date(’Y-m-d’);
    $date2 = ‘2006-08-15?;
    $days = (strtotime($date1) – strtotime($date2)) / (60 * 60 * 24);

    Categories
    HTML MySQL PHP

    PHP OOPS Interview Questions & Answers

    PHP OOPS Interview Questions & Answers

    1) Explain what is object oriented programming language?
    Object oriented programming language allows concepts such as modularity, encapsulation, polymorphism and inheritance.  Objects are said to be the most important part of object oriented language. Concept revolves around making simulation programs around an object. Organize a program around its data (object)& set well define interface to that data. i.e. objects and a set of well defined interfaces to that data. OOP is the common abbreviation for Object-Oriented Programming.  OOps have many properties such as DataHiding,Inheritence,Data Absraction,Data Encapsulation and many more.
    2) Name some languages which have object oriented language and characteristics?
    Some of the languages which have object oriented languages present in them are ABAP, ECMA Script, C++, Perl, LISP, C#, Tcl, VB, Ruby, Python, PHP, etc. Popularity of these languages has increased considerably as they can solve complex problems with ease.
    3) Explain about UML?
    UML or unified modeling language is regarded to implement complete specifications and features of object oriented language. Abstract design can be implemented in object oriented programming languages. It lacks implementation of polymorphism on message arguments which is a OOPs feature.
    4) Explain the meaning of object in object oriented programming?
    Languages which are called as object oriented almost implement everything in them as objects such as punctuations, characters, prototypes, classes, modules, blocks, etc. They were designed to facilitate and implement object oriented methods.
    5) Explain about message passing in object oriented programming?
    Message passing is a method by which an object sends data to another object or requests other object to invoke method. This is also known as interfacing. It acts like a messenger from one object to other object to convey specific instructions.
    6) State about Java and its relation to Object oriented programming?
    Java is widely used and its share is increasing considerably which is partly due to its close resemblance to object oriented languages such as C++. Code written in Java can be transported to many different platforms without changing it. It implements virtual machine.
    7) What are the problems faced by the developer using object oriented programming language?
    These are some of the problems faced by the developer using object oriented language they are: –
    a) Object oriented uses design patterns which can be referred to as anything in general.
    b) Repeatable solution to a problem can cause concern and disagreements and it is one of the major problems in software design.
    8 ) State some of the advantages of object oriented programming?
    Some of the advantages of object oriented programming are as follows: –
    a) A clear modular structure can be obtained which can be used as a prototype and it will not reveal the mechanism behind the design. It does have a clear interface.
    b) Ease of maintenance and modification to the existing objects can be done with ease.
    c) A good framework is provided which facilitates in creating rich GUI applications.
    9 ) Explain about inheritance in OOPS?
    Objects in one class can acquire properties of the objects in other classes by way of inheritance. Reusability which is a major factor is provided in object oriented programming which adds features to a class without modifying it. New class can be obtained from a class which is already present.
    10) Explain about the relationship between object oriented programming and databases?
    Object oriented programming and relational database programming are almost similar in software engineering. RDBMS will not store objects directly and that’s where object oriented programming comes into play. Object relational mapping is one such solution.
    11) Explain about a class in OOP?
    In Object oriented programming usage of class often occurs. A class defines the characteristics of an object and its behaviors. This defines the nature and functioning of a specified object to which it is assigned. Code for a class should be encapsulated.
    12) Explain the usage of encapsulation?
    Encapsulation specifies the different classes which can use the members of an object. The main goal of encapsulation is to provide an interface to clients which decrease the dependency on those features and parts which are likely to change in future. This facilitates easy changes to the code and features.
    13) Explain about abstraction?
    Abstraction can also be achieved through composition. It solves a complex problem by defining only those classes which are relevant to the problem and not involving the whole complex code into play.
    14) Explain what a method is?
    A method will affect only a particular object to which it is specified. Methods are verbs meaning they define actions which a particular object will perform. It also defines various other characteristics of a particular object.
    15) Name the different Creational patterns in OO design?
    There are three patterns of design out of which Creational patterns play an important role the various patterns described underneath this are: –
    a) Factory pattern
    b) Single ton pattern
    c) Prototype pattern
    d) Abstract factory pattern
    e) Builder pattern
    16) Explain about realistic modeling?
    As we live in a world of objects, it logically follows that the object oriented approach models the real world accurately. The object oriented approach allows you to identify entities as objects having attributes and behavior.
    17) Explain about the analysis phase?
    The anlaysis or the object oriented analysis phase considers the system as a solution to a problem in its environment or domain. Developer concentrates on obtaining as much information as possible about the problem. Critical requirements needs to be identified.
    ************************************************************************************************************
    1) Explain the rationale behind Object Oriented concepts?
    Object oriented concepts form the base of all modern programming languages. Understanding the basic concepts of object-orientation helps a developer to use various modern day programming languages, more effectively.
    2) Explain about Object oriented programming?
    Object oriented programming is one of the most popular methodologies in software development. It offers a powerful model for creating computer programs. It speeds the program development process, improves maintenance and enhances reusability of programs.
    3) Explain what is an object?
    An object is a combination of messages and data. Objects can receive and send messages and use messages to interact with each other. The messages contain information that is to be passed to the recipient object.
    4) Explain the implementation phase with respect to OOP?
    The design phase is followed by OOP, which is the implementation phase. OOP provides specifications for writing programs in a programming language. During the implementation phase, programming is done as per the requirements gathered during the analysis and design phases.
    5) Explain about the Design Phase?
    In the design phase, the developers of the system document their understanding of the system. Design generates the blue print of the system that is to be implemented. The first step in creating an object oriented design is the identification of classes and their relationships.
    6) Explain about a class?
    Class describes the nature of a particular thing. Structure and modularity is provided by a Class in object oriented programming environment. Characteristics of the class should be understandable by an ordinary non programmer and it should also convey the meaning of the problem statement to him. Class acts like a blue print.
    7) Explain about instance in object oriented programming?
    Every class and an object have an instance. Instance of a particular object is created at runtime. Values defined for a particular object define its State. Instance of an object explains the relation ship between different elements.
    8 ) Explain about inheritance?
    Inheritance revolves around the concept of inheriting knowledge and class attributes from the parent class. In general sense a sub class tries to acquire characteristics from a parent class and they can also have their own characteristics. Inheritance forms an important concept in object oriented programming.
    9) Explain about multiple inheritance?
    Inheritance involves inheriting characteristics from its parents also they can have their own characteristics. In multiple inheritance a class can have characteristics from multiple parents or classes. A sub class can have characteristics from multiple parents and still can have its own characteristics.
    10) Explain about encapsulation?
    Encapsulation passes the message without revealing the exact functional details of the class. It allows only the relevant information to the user without revealing the functional mechanism through which a particular class had functioned.
    11) Explain about abstraction?
    Abstraction simplifies a complex problem to a simpler problem by specifying and modeling the class to the relevant problem scenario. It simplifies the problem by giving the class its specific class of inheritance. Composition also helps in solving the problem to an extent.
    12) Explain the mechanism of composition?
    Composition helps to simplify a complex problem into an easier problem. It makes different classes and objects to interact with each other thus making the problem to be solved automatically. It interacts with the problem by making different classes and objects to send a message to each other.
    13) Explain about polymorphism?
    Polymorphism helps a sub class to behave like a parent class. When an object belonging to different data types respond to methods which have a same name, the only condition being that those methods should perform different function.
    14) Explain about overriding polymorphism?
    Overriding polymorphism is known to occur when a data type can perform different functions. For example an addition operator can perform different functions such as addition, float addition etc. Overriding polymorphism is generally used in complex projects where the use of a parameter is more.
    15) Explain about object oriented databases?
    Object oriented databases are very popular such as relational database management systems. Object oriented databases systems use specific structure through which they extract data and they combine the data for a specific output. These DBMS use object oriented languages to make the process easier.
    16) Explain about parametric polymorphism?
    Parametric polymorphism is supported by many object oriented languages and they are very important for object oriented techniques. In parametric polymorphism code is written without any specification for the type of data present. Hence it can be used any number of times.
    17) What are all the languages which support OOP?
    There are several programming languages which are implementing OOP because of its close proximity to solve real life problems. Languages such as Python, Ruby, Ruby on rails, Perl, PHP, Coldfusion, etc use OOP. Still many languages prefer to use DOM based languages due to the ease in coding.
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