help on HFJ exercise

[vidu sri]

 
public class m
{
  public static void main(String[] args)
  {
   monster[] ma = new monster[2];
   ma[0]=new monster();
   ma[1]=new vampire();
    for(int x=0;x<2;x++)
    { 
      ma[x].frighten(x);
            }
                }
                   }

class monster
{
  boolean frighten(int z)
  {
    System.out.println("arrrgh");
    return true;
            }
               }
class vampire extends monster
{
  boolean frighten(byte b)
  {
    System.out.println("a bite?");
    return true;
             }
               }

                                                                                                                 

   

if object is created for both the classes and method is called,why the output is arrrgh arrrgh instead of
arrrgh and a bite?.

i could understand that the arguement differs and byte could not hold int,but still could not guess why the input is as like stated above.

[Rob Spoor]

Because vampire's frighten method is overloaded, not overridden. The monster class doesn't know anything about that method.

[Jeanne Boyarsky]

Vidu,
Let's walk through what the JVM "thinks" starting with the loop.
1) First iteration. I see you have this monster object and want to call frighten() on it with an int.
2) I see that method - I'll call it and print out "arrrgh".
3) Second iteration. I see you have this vampire object and want to call frighten() on it with an int.
4) I'll start by looking for matches in the subclass. Vampire has a frighten() method. I can't use it though since I have an int to pass and vampire only takes in a byte.
5) Moving on to the superclass - monster. Now I have a match.

[Bhagat Singh Rawat]

if object is created for both the classes and method is called,why the output is arrrgh arrrgh instead of
arrrgh and a bite?.

i could understand that the arguement differs and byte could not hold int,but still could not guess why the input is as like stated above.

1- ma[0] = new monster();
2- ma[1] = new vampire();

See in 1st case you are creating an instance of monster and in 2nd case you creating instance of child class and assigning to parent class which is known as Polymorphism, therefore you are getting the same result in both cases. It means in the both cases the frighten method of monster class get called.