Static Nested Class in Java

Last Updated: 20 November, 2023

A class that is defined inside another class with the static keyword is known as a static nested class in Java. A static nested class is not associated with any particular instance of the outer class. This means that a static nested class can be accessed and instantiated without having to create an instance of the outer class.

Static nested classes can access static members of the enclosing class, including private members as well, but static nested classes cannot access outer non-static properties directly.

Syntax: Static Nested Class in Java

  class OuterClass {
      // code
      static class NestedStaticClass {
          // code
      }
  }

Important points about Static Nested class in Java

A static nested class is a member of its enclosing class.
A static nested class can have static and non-static fields and methods.
A static nested class cannot access non-static members of its enclosing class.
A static nested class can access static members of its enclosing class, including private members.
An outer class will never be a static class in Java.
To access a static nested class, we can use the following syntax:
OuterClass.StaticNestedClass instance = new OuterClass.StaticNestedClass();

Here's an example of a static nested class in Java:

Example 1 : Static Nested Class implementation in Java

  class OuterClass {
    void display() {
      System.out.println("OuterClass - display() method");
    }
    
    // static inner class
    static class NestedStaticClass {
      // Non-Static Variable
      int num1 = 10;
      // Static Variable
      static int num2 = 20;
      
      // Non-Static Method
      void nonStaticMethod() {
        System.out.println("num1 : " + num1);
      }
      // Static Method
      static void staticMethod() {
        System.out.println("num2 : " + num2);
      }
    }
  }
  
  public class StaticNestedClassExample {
    public static void main(String[] args) {
      
      // Calling NestedStaticClass static method
      OuterClass.NestedStaticClass.staticMethod();
      
      // Creating object of Static Inner Class
      OuterClass.NestedStaticClass innerObject = new OuterClass.NestedStaticClass();
      
      // Calling Non-Static Method of NestedStaticClass
      innerObject.nonStaticMethod();
      
      // Creating object of OuterClass
      OuterClass outerObject = new OuterClass();
      
      // Calling OuterClass method
      outerObject.display();
    }
  }

Output

num2 : 20
num1 : 10
OuterClass - display() method

Example 2 : Static Nested Class access Outer Class static properties

  class OuterClass {
    // Static Variable
    static int num = 20;
    // Static Method
    static void display() {
      System.out.println("OuterClass - static display() method");
    }
    
    static class NestedStaticClass {
      // Static Method
      static void staticMethod() {
        // Accessing OuterClass static properties
        display();
        System.out.println("num : " + num);
      }
    }
  }
  
  public class StaticNestedClassExample2 {
    public static void main(String[] args) {
      // Calling NestedStaticClass static method
      OuterClass.NestedStaticClass.staticMethod();
    }
  }

Output

OuterClass - static display() method
num : 20

Static Nested Class - Interview Questions and Answers

Does Java support top-level classes as static?

Ans. No, Java does not allow us to define a top-level class as static, and if we try to do so, we will get a compile-time exception.

Let's see this scenario through the given example.

static class Test { void show() { System.out.println("show() method"); } } public class StaticOuterClass { public static void main(String[] args) { Test obj = new Test(); obj.show(); } }

Output

Exception in thread "main" java.lang.Error: Unresolved compilation problem: Illegal modifier for the class A; only public, abstract & final are permitted at com.javabytechie.staticnestedclass.A(StaticOuterClass.java:3) at com.javabytechie.staticnestedclass.StaticOuterClass.main(StaticOuterClass.java:11)

Static Nested Class in Java

Static Nested Class - Interview Questions and Answers

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