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Inheritance Basics

To inherit a class, you can use the extends keyword.

The following program creates a superclass called Base and a subclass called Child.

 
class Base {
  int i, j;
  void showBase() {
    System.out.println("i and j: " + i + " " + j);
  }
}
class Child extends Base {
  int k;
  void showChild() {
    System.out.println("k: " + k);
  }
  void sum() {
    System.out.println("i+j+k: " + (i + j + k));
  }
}

public class Main {
  public static void main(String args[]) {
    Base superOb = new Base();
    Child subOb = new Child();

    superOb.i = 10;
    superOb.showBase();
    System.out.println();

    subOb.i = 7;
    subOb.showBase();
    subOb.showChild();
    System.out.println();

    subOb.sum();
  }
}

The output from this program is shown here:


i and j: 10 0

i and j: 7 0
k: 0

i+j+k: 7

The subclass Child includes all of the members of its superclass

The general form of a class declaration that inherits a superclass is shown here:


class subclass-name extends superclass-name { 
   // body of class 
}

You can only have one superclass for any subclass.

Java does not support the multiple inheritance. A class can be a superclass of itself.

A Superclass Variable Can Reference a Subclass Object

For example, consider the following:

 
class Rectangle {}

class ColorRectangle extends Rectangle {}

public class Main {
  public static void main(String args[]) {
    Rectangle rectangle = new Rectangle();
    ColorRectangle colorRectangle = new ColorRectangle();

    rectangle = colorRectangle;

  }
}

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