covariant return - easy example .

[ankur rathi]

class First {
public First my() {
return null ;
}
}
class Second extends First{
public Second my() {
return null;
}
}

This code will not give any compilation error in 1.5 . Right ?
Because Second is a subclass of First . And in 1.5 you can override method just by change the return type ( ofcourse it should be compatable with original ) .

Is everything is right ?
Is this is sufficient for covariant return in beta exam ?

thanks a lot .

[Joyce Lee]

Yes, the code above is legal in 1.5 as long as the return type of an overriding method is a subclass of the return type of an overridden method.

public class First {
public Object my() {
System.out.println("First: my()");
return null ;
}
public static void main(String[] args) {
First o = new Second();
o.my(); // which my() is called?
}
}
class Second extends First {
public String my() {
System.out.println("Second: my()");
return null;
}
}

So what is the output for the above code?

There is an article on covariant parameter types.

[ankur rathi]

I think the output will be :
Second: my()

Logic is same as other overridding methods ...

[ankur rathi]

Thanks a lot Joyce ...

[Joyce Lee]

 

I think the output will be :
Second: my()

Logic is same as other overridding methods ...

Correct.

[Christian Joseph]

yap second.my coz its overriding..

thanks for this post, i understand it now after a 15 minutes of searching the net!

[Bryan Cut]

Thank you for answering this. I am prepping for the SCJP6 and this was touched on in the text