Inner Classes

The Java programming language allows you to define a class within a class. Such a class is called a nested class or inner class.

The advantage of nested classes are used to develop more readable and maintainable code because it logically grouped with in the classes.

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Types of Inner classes

There are two type of inner classes

1.      Static inner class

2.      Non-static inner class

Static inner class

Static inner class is declared with static modifier, refer below code snippet-

/**

 * In this example outter class contains StaticInner class

 * @author Manoj

 */

public class OutterClass {

  public static void main(String[] args) {

     OutterClass.StaticInner staticInner = new OutterClass.StaticInner();

     System.out.println(staticInner.getValue());

  }

  static class StaticInner {

     public String getValue() {

           return "I am static inner class";

     }

  }

}

Non-static inner class-

There are three type of non-static inner class.

1.      Member class

2.      Local class

3.      Anonymous class

Member class

Member class are also define as a member of class, they can access all methods and members of outter class. Refer below code snippet-

/**

 * In this example outter class contains member Inner class

 * @author Manoj

 */

public class OutterClass {

  public static void main(String[] args) {

     OutterClass.MemberInner memberInner = new OutterClass().new MemberInner ();

     System.out.println(memberInner.getValue());

  }

   class MemberInner {

     public String getValue() {

           return "I am member inner class";

     }

  }

}

Local class

Local classes are declared within a block of code or with in a method and are visible only within that block or method, refer below code snippet –

/**

 * In this example outter class contains method local Inner class

 * @author Manoj

 */

public class OutterClass {

  public static void main(String[] args) {

     class LocalInner {

           public String getValue() {

                return "I am in a method local inner class";

           }

     }

     LocalInner localInner = new LocalInner();

     System.out.println(localInner.getValue());

  }

}

Note – Method local inner class can access only final local variable

Anonymous class

An anonymous class is a local class that has no name.

Code snippet for anonymous class-

/**

 * In this example we are creating an anonymous class

 * @author Manoj

 */

public class OutterClass {

  public static void main(String[] args) {

     Runnable runnable = new Runnable() {

           public void run() {

                System.out.println("I am anonymous class");

           }

     };

     runnable.run();

  }

}