Java - Inheritance and Early Binding

What is Early Binding

In early binding, the decision about which method code and field to use is made at compile time.

Early binding is used for the following types of methods and fields of a class in Java:

  • static and non-static fields
  • Static methods
  • Non-static final methods

Demo

class MySuper {
  // An instance variable
  public String str = "MySuper";

  // A static variable
  public static int count = 100;

  public static void print() {
    System.out.println("Inside MySuper.print()");
  }/*from   www  . ja  v  a  2 s .c om*/
}

class MySub extends MySuper {
  // An instance variable
  public String str = "MySub";

  // A static variable
  public static int count = 200;

  public static void print() {
    System.out.println("Inside MySub.print()");
  }
}

public class Main {
  public static void main(String[] args) {
    MySuper ebSuper = new MySuper();
    MySub ebSub = new MySub();

    // Will access MySuper.str
    System.out.println(ebSuper.str);

    // Will access MySuper.count
    System.out.println(ebSuper.count);

    // Will access MySuper.print()
    ebSuper.print();

    // Will access MySub.str
    System.out.println(ebSub.str);

    // Will access MySub.count
    System.out.println(ebSub.count);

    // Will access MySub.print()
    ebSub.print();

    // Will access MySuper.str
    System.out.println(((MySuper) ebSub).str);

    // Will access MySuper.count
    System.out.println(((MySuper) ebSub).count);

    // Will access MySuper.print()
    ((MySuper) ebSub).print();

    // Assign the ebSub to ebSuper
    ebSuper = ebSub; // Upcasting

    /*
     * Now access methods and fields using ebSuper variable, which is referring
     * to a MySub object
     */

    // Will access MySuper.str
    System.out.println(ebSuper.str);

    // Will access MySuper.count
    System.out.println(ebSuper.count);

    // Will access MySuper.print()
    ebSuper.print();
  }
}

Result