TestOverrideOverload.java

import java.io.*;

public class TestOverrideOverload {

   public static void main (String[] args) throws IOException {
      SubBase sub  = new SubBase(1);
      Base    base = sub;
               
      // Java compiler computes access to member variables 
      // at compile time
      System.out.println(base.x);  //9
      System.out.println(sub .x);  //0
               
      // Java dynamically binds methods at runtime
      System.out.println(base.doSomething(3.0, 5));  //8
      System.out.println(sub .doSomething(3.0, 5));  //8
               
      System.out.println(sub .doSuperSomething(3.0, 5)); //17
               
      // Method doSuperSomething(double, int) not found 
      // in class Base
      //System.out.println(base.doSuperSomething(3.0, 5));  
      
      // be very careful to see the result and think why?
      // Change f() to public in Base and SubBase, then run it again
      // notice the difference in output
      SubSubBase c = new SubSubBase(1);
      System.out.println(c.g());

      System.in.read();
   }
}

class Base {
   int cnt;
   int x = 9;
   
   Base(int n) {
      cnt = n;
   }
   
   private int f() { return 0;}
   
   void doSomething(int n) {
   }
   
   // different signature is oK
   int doSomething(double d) {
      return (int)d;
   }
   
   // Methods can't be redefined with a different return type
   //int doSomething(int n) {
   //   return n;
   //}
   
   int doSomething(double d, int a) {
      return (int)d + a + x;
   }
   public void m() {
   }   
}

class SubBase extends Base{
   int x;
   
   SubBase(int n){
      // this must be explicitly called
      super(n);
   }
   
   private int f() { return 1;}
   public  int g() { return f();}
   
   // Methods can't be redefined with a different return type
   //int doSomething(int n) {
   //   return n;
   //}
   
   int doSomething(double d, int a) {
      return (int)d + a + x;
   }
   
   int doSuperSomething(double d, int a) {
      return super.doSomething(d, a);
   }
   
   // method can't be overriden to be more private
   //protected void m() {
   //}   
}

class SubSubBase extends SubBase{
   SubSubBase(int n){
      // this must be explicitly called
      super(n);
   }
   public int f() { return 2;}
}