Java Member Inner class

A non-static class that is created inside a class but outside a method is called member inner class. It is also known as a regular inner class. It can be declared with access modifiers like public, default, private, and protected.

Syntax:

class Outer{
 //code
 class Inner{
  //code
 }
}

Java Member Inner Class Example

In this example, we are creating a msg() method in the member inner class that is accessing the private data member of the outer class.

TestMemberOuter1.java

class TestMemberOuter1{
 private int data=30;
 class Inner{
  void msg(){System.out.println("data is "+data);}
 }
 public static void main(String args[]){
  TestMemberOuter1 obj=new TestMemberOuter1();
  TestMemberOuter1.Inner in=obj.new Inner();
  in.msg();
 }
}

Test it Now

Output:

data is 30

How to instantiate Member Inner class in Java?

An object or instance of a member's inner class always exists within an object of its outer class. The new operator is used to create the object of member inner class with slightly different syntax.

The general form of syntax to create an object of the member inner class is as follows:

Syntax:

Example:

Here, OuterClassReference is the reference of the outer class followed by a dot which is followed by the new operator.

Internal working of Java member inner class

The java compiler creates two class files in the case of the inner class. The class file name of the inner class is "Outer$Inner". If you want to instantiate the inner class, you must have to create the instance of the outer class. In such a case, an instance of inner class is created inside the instance of the outer class.

Internal code generated by the compiler

The Java compiler creates a class file named Outer$Inner in this case. The Member inner class has the reference of Outer class that is why it can access all the data members of Outer class including private.

import java.io.PrintStream;
class Outer$Inner
{
    final Outer this$0;
    Outer$Inner()
    {   super();
        this$0 = Outer.this;
    }
    void msg()
    {
        System.out.println((new StringBuilder()).append("data is ")
                    .append(Outer.access$000(Outer.this)).toString());
    }
}

Next TopicJava Anonymous Inner class

← prev next →