Nested Class: Class defined within another class is called nested class. Nested class is divided into two parts-

1.Static

2.Non-static Static nested class is declared static. Non-static nested class is also called inner class.

Example:

public class NestedClass{
    private String outer = "Outer Class"; //NestedClass instance variable
    InnerClass innerClass = new InnerClass();
    void getOuterS(){
        System.out.println(outer); 
    }
    void getInnerS(){
        System.out.println(innerClass.inner);
    }
    class InnerClass{
        private String inner = "Inner Class"; //InnerClass instance variable, uninitialized
        void getInnerS(){
            System.out.println(inner);
        }
        void getOuterS(){
            System.out.println(NestedClass.this.outer);
        }
    }
    public static void main(String[] args){
        NestedClass nestedClass = new NestedClass();
        NestedClass.InnerClass nestedInner = nestedClass.new InnerClass();//can also be new NestedClass().new InnerClass ();
        nestedClass.getOuterS();
        nestedClass.getInnerS();
        nestedInner.getInnerS();
        nestedInner.getOuterS();
    }
}