Polymorphism

[akila sekaran]

class Base {
    public void whereAmI() { System.out.println("In Base"); }
}

class Derived extends Base {
    public void whereAmI() { System.out.println("In Derived"); }
}

public class Polymorphism {
    public static void main(String[] args) {
        Base base = new Base();
        base.whereAmI();
        base = new Derived();
        base.whereAmI();
    }
}

o/p is 
In Base
In Base

How ???

[Henry Wong]

akila sekaran wrote:

class Base {
    public void whereAmI() { System.out.println("In Base"); }
}

class Derived extends Base {
    public void whereAmI() { System.out.println("In Derived"); }
}

public class Polymorphism {
    public static void main(String[] args) {
        Base base = new Base();
        base.whereAmI();
        base = new Derived();
        base.whereAmI();
    }
}

o/p is 
In Base
In Base

How ???

My output ...

In Base
In Derived

Henry

[Eswar Nec]

Hi akila,

I test your code. My output is also

In Base
In Derived

[Jelle Klap]

Are you sure this is the exact code, copied and pasted directly from the .java file?
I could imagine the code you're actually running has a typo or character case difference in the method name in the Derived class, which would mean it's not actually an override of the Base calss' method.
To avoid situations like that it's very usefull to tag a method that is intended to be an override (or interface implementation as of Java 6) with the @Override annotation, like this:

class Base {  
    public void whereAmI() { System.out.println("In Base"); }  
}  


class DerivedA extends Base {  
    @Override
    public void whereAmI() { System.out.println("In DerivedA"); } // Valid override, compiles fine
}

class DerivedB extends Base {
    @Override  
    public void whereAmi() { System.out.println("In DerivedB"); }  // Compiler error!
                                          //  Not a valid override, notice the lowercase i
}  

[Winston Gutkowski]

Jelle Klap wrote:like this:...

Jelle: just a reminder not to put enormously long lines in code blocks
I split yours up.

Winston

[Randall Twede]

it has happened to me before. perhaps when you compiled you compiled the "main" class and assumed it would also recompile a class it depended on, but there was already a class file by that name so it didn't recompile the helper class.