• Post Reply
  • Bookmark Topic Watch Topic
  • New Topic

Question regarding method signature and overriding.

 
Rajkamal Pillai
Ranch Hand
Posts: 445
1
Java Spring
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Hello,

Methods cannot be overloaded based on the return types alone. That makes sense as the compiler will not be in a position to differentiate which method is invoked.

In the case of overriding something similar is applicable. Why cannot a method which is overriding in a derived class not permitted to have a different return type? The compiler will be able to make out the overriding method but then why does it care about the return types matching?

Cheers,
Raj.

 
Jesper de Jong
Java Cowboy
Saloon Keeper
Posts: 15452
42
Android IntelliJ IDE Java Scala Spring
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Because of polymorphism. You could have a variable of the type of the superclass which actually refers to an instance of the subclass. Suppose you could do this:

Then look at this:
 
Miklos Szeles
Ranch Hand
Posts: 142
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Jesper is absolutely right. Just one note:
From Java 5 you can use covariant return types.
It means that a method in a subclass may return an object whose type is a subclass of the type returned by the method with the same signature in the superclass.
 
Rob Spoor
Sheriff
Pie
Posts: 20611
63
Chrome Eclipse IDE Java Windows
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Which can be of great use in methods like clone(). For instance, Date.clone() could have returned a Date, thereby removing the need for casts. Sun however were either lazy or they simply forgot to change the declared return types for just about every method that could have used it. It's not like returning Date from Date.clone() would have broken any code, it just would have made all the casts unnecessary.
 
Rajkamal Pillai
Ranch Hand
Posts: 445
1
Java Spring
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Thanks everyone!
 
  • Post Reply
  • Bookmark Topic Watch Topic
  • New Topic