Inner Class in Java

Inner class in a class defined as a class inside another class. So it is itself a class but first it will act as a member of that class. As we know that we cannot make a class as static but inner class can be made as static which proves that it is first a member of a class in which it is defined . We can execute our class with its name but to execute a inner class we need to take help of outer class that proves that an inner class has identity with its outer class.

Important points regarding Inner Class :

1. A .class file is generated  for inner class but the file name will be as follows :
    < outer_class_name > $ < inner_class_name > . class 

2. We can be able to create a reference of inner class within the scope of an outer class simply as a normal reference definition.

3. To create a reference of inner class outside the scope of an outer class then we need to indicate to write the inner class name followed by outer class name, like this
     < outer_class_name > . < inner_class_name > . < ref_value > = null ;

4. As inner class itself is a member of a outer class then it the other members won't be the member of the inner class.

5. We can have a class inside an inner class which is defined as the inner class of inner class.So like this we can have infinite number of inner class / nested classes.

6. Inner class is generally used for abstraction.

Example of an inner class :- 

class prog {    // main class 

int x;

class A {      // Inner class of prog 

int x ;
String name ;

public static void main( String sush[] ) {

System.out.println(" Inner class " ) ;
A a = new A();     // Object of an inner class 
  }

}

In the above example class A is an inner class of prog class which is also called as the instance class.

Types of Inner class :

There are four (4) types of inner class :

1. Instance inner class.  -->     Click here to know more about instance inner class
2. Static inner class.      -->     Click here to know more about Static inner class
3. Local Inner class       -->    Click here to know more about Local inner class
4. Anonymous inner class.