> Java > Member Inner Class

Member Inner Class in Java

Last Updated: 04 February, 2023

A class that is defined inside another class without a static keyword and outside a method is known as a "member inner class" in Java.

A member inner class is defined as a member of the outer class, the same as variables and methods.
A member inner class can be public, private, or protected in Java.
A member inner class can access all the properties (variables and methods) of an outer class, even private also.
A member inner class provides more readable and maintainable code because it logically groups classes and interfaces in one place.

Syntax of Member Inner Class:

  class OuterClass {
    // variables
    // methods
    
    // Defining a class inside another class as member 
    class InnerClass {
      // variables
      // methods
    }
  }

To access inner class properties first, we need to create an instance of an outer class because the inner class is defined as a member of the outer class. Using the outer class instance, we create the instance of the inner class.

  // Creating an object of Outer class
  OuterClass outObj = new OuterClass();
  
  // Using outer class object creating inner class object
  OuterClass.InnerClass innObj = outObj.new InnerClass();

Let's understand the implementation of member inner class with the help of the given example.

Example: Member Inner Class in Java

  class OuterClass {
    String name = "John";
    private int age = 25;
  
    public void display() {
      System.out.println("Outer Class - display() method");
    }
  
    // Member Inner Class
    class InnerClass {
      String city = "Bengaluru";
  
      public void show() {
        System.out.println("Name : " + name);
        System.out.println("Age : " + age);
        System.out.println("City : " + city);
  
        // Accessing Outer class display() method
        display();
      }
    }
  }
  
  public class MemberInnerClassExample {
    public static void main(String[] args) {
  
      // Creating an object of Outer class
      OuterClass outObj = new OuterClass();
  
      // Using outer class object creating inner class object
      OuterClass.InnerClass innObj = outObj.new InnerClass();
  
      outObj.display();
      innObj.show();
  
      // outObj.show(); --> Not allowed in Java
      // innObj.display(); --> Not allowed in Java
    }
  }

Output

Outer Class - display() method
Name : John
City : Bengaluru
Outer Class - display() method

What compiler does at compile time:

When we compile the above Java program, after successful compilation, the compiler generates three .class files for the each classes. These files are named by the compiler as:

Outer.class
OuterClass$InnerClass.class
MemberInnerClassExample.class

👉 Before Compilation

👉 After Compilation

That's all guys, hope this Java article is helpful for you.

Happy Learning... 😀

Please share this article on social media to help others.

If you have any query or suggestion regarding this artical please share with us
feedback@javabytechie.com

Member Inner Class - Interview Questions and Answers

Can inner classes access private members of outer class?

Non-static nested classes (inner classes) have access to other members of the enclosing class, even if they are declared private.

How many inner classes we can define inside the outer class?

We can define any number of inner classes in the outer class; there is no programmatic limit, but inner classes should be defined based on the project's business requirements.

Member Inner Class in Java

Member Inner Class - Interview Questions and Answers

Currently No Video available