jQuery overview - jQuery basic tutorial series 1

jQuery Introduction :

jQuery is a fast and concise JavaScript Library created by John Resig in 2006 with a nice motto: Write less, do more.
jQuery simplifies HTML document traversing, event handling, animating, and Ajax interactions for rapid web development.
jQuery is a JavaScript toolkit designed to simplify various tasks by writing less code. Here is the list of important core features supported by jQuery:

  • DOM manipulation: The jQuery made it easy to select DOM elements, traverse them and modifying their content by using cross-browser open source selector engine called Sizzle.
  • Event handling: The jQuery offers an elegant way to capture a wide variety of events, such as a user clicking on a link, without the need to clutter the HTML code itself with event handlers.
  • AJAX Support: The jQuery helps you a lot to develop a responsive and feature-rich site using AJAX technology.
  • Animations: The jQuery comes with plenty of built-in animation effects which you can use in your websites.
  • Lightweight: The jQuery is very lightweight library - about 19KB in size ( Minified and gzipped ).
  • Cross Browser Support: The jQuery has cross-browser support, and works well in IE 6.0+, FF 2.0+, Safari 3.0+, Chrome and Opera 9.0+
  • Latest Technology: The jQuery supports CSS3 selectors and basic XPath syntax.

  • How to use jQuery library?

    Now you can include jquery library in your HTML file as follows:
    <html>
<head>
<title>The jQuery Example</title>
   <script type="text/javascript" 
   src="/jquery/jquery-1.3.2.min.js"></script>
   <script type="text/javascript">
      // you can add our javascript code here 
   </script>   
</head>
<body>
........
</body>
</html>

    How to call a jQuery library functions?

    As almost everything we do when using jQuery reads or manipulates the document object model (DOM), we need to make sure that we start adding events etc. as soon as the DOM is ready.
    If you want an event to work on your page, you should call it inside the $(document).ready() function. Everything inside it will load as soon as the DOM is loaded and before the page contents are loaded.
    To do this, we register a ready event for the document as follows:
    $(document).ready(function() { // do stuff when DOM is ready });
  • To call upon any jQuery library function, use HTML script tags as shown below:
<html>
<head>
<title>The jQuery Example</title>
   <script type="text/javascript" 
   src="/jquery/jquery-1.3.2.min.js"></script>
   
   <script type="text/javascript" language="javascript">
   // <![CDATA[
   $(document).ready(function() {
      $("div").click(function() {
        alert("Hello world!");
      });
   });
   // ]]>
   </script>

</head>
<body>
<div id="newdiv">
Click on this to see a dialogue box.
</div>
</body>
</html>

    How to use Custom Scripts?

    It is better to write our custom code in the custom JavaScript file : custom.js, as follows:
  •     
    /* Filename: custom.js */
$(document).ready(function() {
  $("div").click(function() {
 alert("Hello world!");
  });
});
Now we can include custom.js file in our HTML file as follows:

<html>
<head>
<title>The jQuery Example</title>
   <script type="text/javascript" 
   src="/jquery/jquery-1.3.2.min.js"></script>
   <script type="text/javascript" 
   src="/jquery/custom.js"></script>
</head>
<body>
<div id="newdiv">
Click on this to see a dialogue box.
</div>
</body>
</html>
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Check if a class extends another at Runtime : Java

Summary :

  • If you want to know whether or not a Class extends another, use Class#isAssignableFrom(Class)
  • Class#isAssignableFrom(Class) also returns true if both classes are same
  • To find if an object is instance of a class use instanceof operator
  • To know if a class is direct sub class of another class then use Class#getSuperClass().equals(Class)

Setup :

We have an interface MyInterface and three classes MyBaseClass, MySubClass and SomeOtherClass with the below hierarchy.

interface MyInterface {
}

class MyBaseClass implements MyInterface {
}

class MySubClass extends MyBaseClass {
}

class SomeOtherClass {
}

Tests:

   

public class Test {
  
  public static void main( String[] args ) {
    
    /*
     * Checking if a class is same as or is a superclass or superinterface
     * 
     * of another class (the class in parameter)
     */
    System.out.println( MyBaseClass.class.isAssignableFrom( MyBaseClass.class ) );// true : same class
    System.out.println( MyBaseClass.class.equals( MyBaseClass.class ) );// true : same class
    System.out.println( MyBaseClass.class.isAssignableFrom( MySubClass.class ) );// true : superclass
    System.out.println( MyInterface.class.isAssignableFrom( MySubClass.class ) );// true : superinterface
    System.out.println( MyBaseClass.class.isAssignableFrom( SomeOtherClass.class ) );// false : the two classes has no relation
    System.out.println( MySubClass.class.isAssignableFrom( MyBaseClass.class ) );// false : MySubClass is not the superclass
    
    /*
     * Checking if a object is instance of a class
     */
    
    IMyInterface object = new MyBaseClass( );
    System.out.println( object instanceof MyInterface ); // true
    System.out.println( object instanceof MyBaseClass ); // true
    System.out.println( object instanceof MySubClass ); // false
    System.out.println( object instanceof SomeOtherClass );// false
    
    /*
     * check if a class is direct superclass of another
     */
    
    System.out.println( MySubClass.class.getSuperclass( ).equals( MyInterface.class ) );// false : its not a directsuper class, interface
    System.out.println( MyBaseClass.class.getSuperclass( ).equals( MyInterface.class ) );// false : its not a directsuper class, interface
    System.out.println( MySubClass.class.getSuperclass( ).equals( MyBaseClass.class ) );// true : MyBaseClass is extending MySubClass
  }
}

Full code : 

   

public class Test {
  
  public static void main( String[] args ) {
    
    /*
     * Checking if a class is same as or is a superclass or superinterface
     * 
     * of another class (the class in parameter)
     */
    System.out.println( MyBaseClass.class.isAssignableFrom( MyBaseClass.class ) );// true : same class
    System.out.println( MyBaseClass.class.equals( MyBaseClass.class ) );// true : same class
    System.out.println( MyBaseClass.class.isAssignableFrom( MySubClass.class ) );// true : superclass
    System.out.println( MyInterface.class.isAssignableFrom( MySubClass.class ) );// true : superinterface
    System.out.println( MyBaseClass.class.isAssignableFrom( SomeOtherClass.class ) );// false : the two classes has no relation
    System.out.println( MySubClass.class.isAssignableFrom( MyBaseClass.class ) );// false : MySubClass is not the superclass
    
    /*
     * Checking if a object is instance of a class
     */
    
    IMyInterface object = new MyBaseClass( );
    System.out.println( object instanceof MyInterface ); // true
    System.out.println( object instanceof MyBaseClass ); // true
    System.out.println( object instanceof MySubClass ); // false
    System.out.println( object instanceof SomeOtherClass );// false
    
    /*
     * check if a class is direct superclass of another
     */
    
    System.out.println( MySubClass.class.getSuperclass( ).equals( MyInterface.class ) );// false : its not a directsuper class, interface
    System.out.println( MyBaseClass.class.getSuperclass( ).equals( MyInterface.class ) );// false : its not a directsuper class, interface
    System.out.println( MySubClass.class.getSuperclass( ).equals( MyBaseClass.class ) );// true : MyBaseClass is extending MySubClass
  }
}

interface MyInterface {
}

class MyBaseClass implements MyInterface {
}

class MySubClass extends MyBaseClass {
}

class SomeOtherClass {
}
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superclass "javax.servlet.http.HttpServlet" not found on Java Build Path - solution

You might (normally) get the error following error on a dynamic java web project created through maven on Eclipse IDE. The solution is simple :
Error : 
The superclass "javax.servlet.http.HttpServlet" was not found on the Java Build Path
Error Location :
<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>
Solution 1)
Edit pom.xml to include servlet-api-x.x.jar in your dependencies:
<dependency>
  <groupId>javax.servlet</groupId>
  <artifactId>javax.servlet-api</artifactId>
  <version>3.1.1</version>
  <scope>provided</scope>
</dependency>
Solution 2)
Go to Project->Properties->Target Runtimes . And add your server container eg. : Apache Tomcat


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Java Obsfucate Password - Replace with asterisk

Obsfucate password : 

Rreplace everything except first and last character by asterisk ( * ), if  the password is less than ALLOWED_LENGTH characters long obfuscate it entirely i.e., prints asterisks

Code : 
   
//Test 
System.out.println( getObfuscatedPassword( "" ) ); //returns null
System.out.println( getObfuscatedPassword( "pwdd" ) ); //returns ****
System.out.println( getObfuscatedPassword( "mySecurePassword" ) ); // returns m**************d


//Method 
public static String getObfuscatedPassword( String password ) {
   
   int ALLOWED_LENGTH = 5;
   
   if ( null == password || "".equals( password.trim( ) ) ) {
    return null;
   }
   
   StringBuilder builder = new StringBuilder( );
   
   if ( password.length( ) < ALLOWED_LENGTH ) {
   
    for ( int i = password.length( ); i != 0; i-- ) {
     builder.append( "*" );
    }
   
    return builder.toString( );
   }
   
   builder.append( password.charAt( 0 ) );
   
   for ( int i = password.length( ) - 2; i != 0; i-- ) {
    builder.append( "*" );
   }
   
   return builder.append( password.substring( password.length( ) - 1 ) ).toString( );
}
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change maven local repository path - symbolic links

Let's suppose we want to change the local maven repo path (default : c:\users\user_name\.m2\repository) to some other real folder - lets say e:\repo  - so that the contents from e:\repo folder are mapped to the default folder location.

This might be useful when .m2 folder on your C: drive is taking too much space. In such case, you can move the content to another drive ( e:\repo) and have a symbolic link on C:\ drive instead - so that all the configuration remains intact.


The following command creates a link folder "repository" in /.m2 folder and points to the source e:\REPO

C:\>mklink /d c:\users\gtiwari\.m2\repository e:\REPO


Note:


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using symbolic links on windows

Using symbolic links (MKLINK comand) on windows:

Suppose we want to create a link of folder 'e:\source' to c:\target\bridge then, use the following command:

C:\>mklink /d c:\target\bridge e:\source

Syntax : mklink /d TARGET SOURCE_DIR

  • This command creates a link folder "bridge" in c:\target\ where you can see the contents from e:\source.
For more info :
Visit: http://ss64.com/nt/mklink.html - 
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