Back to basics - Polymorphism ......

[Jones Iraland]

Hi ,
Can anyone explain to me about the following issue i am having

Its seems in Polymorphism

"Reference variable type determines the methos to be called " and
"Polymorphic method invocation apply only to overidden instance methods."

In overriding it says "Object type not the reference variable type determines which overridden method is used at runtime."

Do you know how this works?


Cheers,
Johns

[Balu Sadhasivam]

Please check out this Javaranch Polymorphism

Say,

A a = new B(); // assuming B is subclass of A

Here A is called refernce type for a and B() is called object type. And with thsi info check out teh above article.

[Jones Iraland]

Hi,
My question is how come if polymorphism invokes methods according to reference variable type and only do overriding ,but in overiding methods invocation happens according to object type and not reference type.

Cheers,
Johns

[Balu Sadhasivam]

Jones

Jones Iraland wrote:Hi,
polymorphism invokes methods according to reference variable type and only do overriding ,but in overiding methods invocation happens according to object type and not reference type.

Cheers,
Johns

If i understood your question correctly.. this is polymorphism..

In overriding it says "Object type not the reference variable type determines which overridden method is used at runtime."

During compile time , compiler checks for the reference type and if it has called methods in it.. only during runtime , the object that gets created will call its own inherited method ( if method is not overridden) or overriden method (if overrideen) . wats your doubt ?

[Jones Iraland]

Hi Balu,
I think i got it.Thanks for explanation.

I wrote this program to get it more clear in my head.

public class Poly extends PolyParent{
public void go(){
System.out.println("Inside Poly");
}
public static void main(String args[]){
PolyParent p=new Poly();

p.go();
}
}

class PolyParent{
public void go(){
System.out.println("Inside PolyParent");
}
}

If I commented PolyParent class go() method it will not compile.when I run this method it realy invokes Poly class go() method.

So Polymorphism happens at compile time actual method will be called depends on run time.

Have I got it correct?

[Balu Sadhasivam]

Yup, you are right !!

try changing access specifers (coderanch, private) to understand overriden rules..

[Jones Iraland]

Thanks Mate cheers

[Guilherme Bazilio]

Jones Iraland wrote:
So Polymorphism happens at compile time actual method will be called depends on run time.

Polymorphims happens at compile time?? Does the action of invoking methods dynamically has anything to do with Polymorphim?