overidden method question

[Manoj Garg]

is the declaration of method duplicate in class Circle valid ?

public class Shape
{
public Shape duplicate()
{
return (Shape)this;
}

}

public class Circle extends Shape
{
public Circle duplicate ()
{
return (Circle)this;
}

}

[Vishwanath Krishnamurthi]

Hi,

You can just compile it and see...

[Noam Wolf]

One hint that helped me a lot was the following:

Reference type determines the overloads.

Object type determines overrides.

So in your example you're defining "duplicate" in Shape and in its subclass "Circle". Since this is an override (it can't be an overload because you have not changed the signature) the compiler will know which class to call which means there is no ambiguity here so it will compile correctly.

Quiz time... where will the call for the following examples come from (Shape or Circle):

 
Shape s = new Shape();
s.duplicate();
 
Circle c = new Circle();
c.duplicate();   
 
Shape sc = new Circle();
sc.duplicate();

If you get this example you're golden.

HTH

[Manoj Garg]

Shape s = new Shape();
s.duplicate(); - duplicate of shape class will be called

Circle c = new Circle();
c.duplicate(); - here duplicate of circle

Shape sc = new Circle();
sc.duplicate(); - here complier will check if duplicate method exists in class shape.. at run time call will be from circle class as it is override.

Thanks.

[Noam Wolf]

well done. So does this mean you understand now?