static nested classes in java

A nested class that is declared static is called a static nested class. Memory to the objects of any static nested classes are allocated independently of any particular outer class object. A static nested class use the instance variables or methods defined in its enclosing class only through an object reference. A static nested class interacts with the instance members of its outer class or any other class just like a top-level class.

Given below is the syntax of the Static nested class that defines static nested class having keyword static in the outer class.

class OuterClass {
  ....
  static class StaticNestedClass {
    ....
  }
  class InnerClass {
  .... 
    }
  }

Static nested classes can be accessed by using the enclosing class name:

uterClass.StaticNestedClass

If we want to make an object of the static nested class then we have to write down the following code:

OuterClass.StaticNestedClass nestedObject = new OuterClass.StaticNestedClass();

Static nested class facts:

• is defined as a static member of the parent class
• accepts all accessibility modifiers
• it is NOT linked to an outer instance (it can live independently)
• has direct access to static members of the parent class regardless of the access modifiers declared in the parent class
• has direct access to all members of an instance of the parent class regardless of the access modifiers declared in the parent class

Program of static nested class that have instance method

class StaticNested{
   static String message = "Dinesh on Java";

  static class Inner{
     void display()
     {
        System.out.println("message is "+message);
     }
  }
 
  public static void main(String args[]){
      StaticNested.Inner obj = new StaticNested.Inner();
      obj.display();
  }
}

output:

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

There are following class files are generated after the compilation of the program.

1. StaticNested$Inner.class
2. StaticNested.class

Internal code generated by the compiler for static nested class

import java.io.PrintStream;

static class StaticNested$Inner
{
    StaticNested$Inner(){
   
    }

   void display(){
      System.out.println((new StringBuilder()).append("message is ")
      .append(StaticNested.message).toString());
   }
    
}

Program of static nested class that have static method

class StaticNested{
   static String message = "Dinesh on Java";

  static class Inner{
     static void display()
     {
        System.out.println("message is "+message);
     }
  }
 
  public static void main(String args[]){
      StaticNested.Inner.display();//no need to create the instance of static nested class
  }
}

output:

The advantage of a static nested class is that it doesn’t need an object of the containing class to work. This can help you to reduce the number of objects your application creates at runtime.