Java Object Oriented Design - Java Inner Class Members

An inner class has access to all instance members, instance fields, and instance methods of its enclosing class.

class Outer {/*from w  w w .  j a v a 2s  .  c  o m*/
  private int value = 2014;
  public class Inner {
    public void printValue() {
      System.out.println("Inner: Value  = " + value);
    }
  } // Inner class ends here

  public void printValue() {
    System.out.println("Outer: Value  = " + value);
  }
  public void setValue(int newValue) {
    this.value = newValue;
  }
}

public class Main {
  public static void main(String[] args) {
    Outer out = new Outer();
    Outer.Inner in = out.new Inner();

    out.printValue();
    in.printValue();

    out.setValue(2015);

    out.printValue();
    in.printValue();
  }
}

The code above generates the following result.

Example

The following code shows how to access inner variable for inner class.

public class Main {
  public static void main(String[] args) {
    Outer out = new Outer();
    Outer.Inner in = out.new Inner();/* www .  j a  v  a 2 s.  c o  m*/

    out.printValue();
    in.printValue();

    out.setValue(3);

    out.printValue();
    in.printValue();
  }
}
class Outer {
  private int value = 1;
  public class Inner {
    private int value = 2;
    public void printValue() {
      System.out.println("Inner: Value  = " + value);
    }
  } // Inner class ends here
  public void printValue() {
    System.out.println("Outer: Value  = " + value);
  }
  public void setValue(int newValue) {
    this.value = newValue;
  }
}

The code above generates the following result.

this keyword for Inner class

The following code shows how to use the keyword this in the inner class.

class Outer {/*w  w w.  j  a va 2  s  .c  om*/
  private int value = 1;
  class QualifiedThis {
    private int value = 2;

    public void printValue() {
      System.out.println("value=" + value);
      System.out.println("this.value=" + this.value);
      System.out.println("QualifiedThis.this.value=" + QualifiedThis.this.value);
    }

    public void printHiddenValue() {
      int value = 2;
      System.out.println("value=" + value);
      System.out.println("this.value=" + this.value);

      System.out.println("QualifiedThis.this.value=" + QualifiedThis.this.value);
    }
  }
  public void printValue() {
    System.out.println("value=" + value);
    System.out.println("this.value=" + this.value);
  }  
}

public class Main {
  public static void main(String[] args) {
    Outer outer = new Outer();
    Outer.QualifiedThis qt = outer.new QualifiedThis();
    System.out.println("printValue():");
    qt.printValue();

    System.out.println("printHiddenValue():");
    qt.printHiddenValue();
    outer.printValue();
  }
}

The code above generates the following result.

Hidden variable

If the instance variable name is hidden, you must qualify its name with the keyword this or the class name as well as the keyword this.

class TopLevelOuter {
  private int v1 = 100;
/*  w  w  w .j  a v  a  2 s .co  m*/
  // Here, only v1 is in scope
  public class InnerLevelOne {
    private int v2 = 200;

    // Here, only v1 and v2 are in scope
    public class InnerLevelTwo {
      private int v3 = 300;

      // Here, only v1, v2, and v3 are in scope
      public class InnerLevelThree {
        private int v4 = 400;

        // Here, all v1, v2, v3, and v4 are in scope

      }
    }
  }
}

From outer class

The following code shows how to reference the variable from the outer class.

public class Test{
  private int value = 1;
  public class Inner {
    private int value = 2;
// w w  w  .j  a v  a  2 s. c  om
    public void printValue() {
      System.out.println("Inner: Value  = " + value);
      System.out.println("Outer: Value  = " + Test.this.value);
    }
  } // Inner class ends here

  public void printValue() {
    System.out.println("\nOuter - printValue()...");
    System.out.println("Outer: Value  = " + value);
  }

  public void setValue(int newValue) {
    System.out.println("\nSetting  Outer's value to " + newValue);
    this.value = newValue;
  }

}