Method Overriding

[swaraj gupta]

class SuperFoo {
  SuperFoo doStuff(int x) {
     return new SuperFoo();
   }
 }

 class Foo extends SuperFoo {  
	Foo doStuff(int x) {
                       return new Foo();
               }
 }

This code compiles successfully, why?
As whatever i know if sub class overrides a super class method then the return type of overriding method must be same as what of overridden method of super class (Compile time error otherwise). Please help

[Mohamed Sanaulla]

swaraj gupta wrote:

class SuperFoo {
  SuperFoo doStuff(int x) {
     return new SuperFoo();
   }
 }

 class Foo extends SuperFoo {  
	Foo doStuff(int x) {
                       return new Foo();
               }
 }

This code compiles successfully, why?
As whatever i know if sub class overrides a super class method then the return type of must be same as what in super class (Compile time error otherwise). Please help

Its using CoVariant Return type. You can return either the same type or sub class of that type. So in this case Foo extends SuperFoo, so where ever a SuperFoo instance is expected we can assign a Foo instance.

[Harikrishna Gorrepati]

Hi Swaraj, Could you please set the status as Yes for "Allow other users to send private messages:" in your My Profile page. I want to send a Private Message (PM)

[swaraj gupta]

thanks mohammed sanaullah,

just one more thing to ask...i have tried this snippet and found that along with what you have said
we can return null as well from the overriding doStuff method of class Foo, may i have the reason for this.. ...

[Ankit Garg]

swaraj gupta wrote:i have tried this snippet and found that along with what you have said
we can return null as well from the overriding doStuff method of class Foo, may i have the reason for this.. ...

null can be type casted into any reference type, so you can return null from any method which returns an object i.e. anything except a primitive...

[swaraj gupta]

thanks ...

[Rohit Ramachandran]

Foo is-a SuperFoo.

Therefore when you're returning a foo, you're returning something that is-a superfoo. Aren't you?