Java static nested class

A static class i.e. created inside a class is called static nested class in java. It cannot access non-static data members and methods. It can be accessed by outer class name.

It can access static data members of outer class including private.
Static nested class cannot access non-static (instance) data member or method.

Static nested class with instance method

Example

snippet

class TestOuter1{
  static int data=30;
  static class Inner{
   void msg(){System.out.println("data is "+data);}
  }
  public static void main(String args[]){
  TestOuter1.Inner obj=new TestOuter1.Inner();
  obj.msg();
  }
}

Output

data is 30

In this example, you need to create the instance of static nested class because it has instance method msg(). But you don't need to create the object of Outer class because nested class is static and static properties, methods or classes can be accessed without object.

Internal class generated by the compiler

snippet

import java.io.PrintStream;
static class TestOuter1$Inner
{
TestOuter1$Inner(){}
void msg(){
System.out.println((new StringBuilder()).append("data is ")
.append(TestOuter1.data).toString());
}  
}

Static nested class with static method

If you have the static member inside static nested class, you don't need to create instance of static nested class.

Example

snippet

class TestOuter2{
  static int data=30;
  static class Inner{
   static void msg(){System.out.println("data is "+data);}
  }
  public static void main(String args[]){
  TestOuter2.Inner.msg();//no need to create the instance of static nested class
  }
}

Output

data is 30