Can an Implementing Class of Foo be called as an extending class of Foo?

Question

This question has been baffling to me; below is an example.

interface class:

public interface UserInterface{

   public String make_nickname();

}

implementing class:

public class UserInfo implements UserInterface{

   private String name;
   private String nickname;

   public String make_nickName(){
   this.nickname = this.name + "ish";
   return this.nickname;
   }


}

That given, I'm calling any instances that implements UserInterface like such:

some arbitrary function in another remote class:

public void showNickName(<T extends UserInterface>T user){
   system.out.println(user.make_nickname());
}

T is used to denote a (generic) implementing class of UserInterface.
But here I called it as <T exnteds UserInterface> which as far as I know implies T is an subclass(not implementing class) of UserInterface.
Is this legitimate grammar of calling instances of UserInfo?
Somehow above code seems to work for me.

Any feedback would be welcome.

I suspect the keyword `extends` was used for this to avoid adding another keyword that meant "extends or implements" to the language grammar. Adding keywords is bad for backwards compatibility, because if you use a word that someone has used as a name for a variable/method/class/etc. then their code will stop working in the new version. Backwards compatibility is an explicit goal for Java language changes. — kaya3, Feb 06 '20 at 06:37

score 2 · Accepted Answer · edited Feb 06 '20 at 06:36

2

As mentioned in the Java tutorial on bounded type parameters:

In generics context, extends is used in a general sense to mean either "extends" (as in classes) or "implements" (as in interfaces).

edited Feb 06 '20 at 06:36

kaya3

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answered Feb 06 '20 at 06:35

Kartik

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thanks. should have researched more before uploading question. Anyway saved me a lot trouble . Thankyou! – Jangwhan Jeong Feb 06 '20 at 06:41

Can an Implementing Class of Foo be called as an extending class of Foo?

interface class:

implementing class:

some arbitrary function in another remote class:

1 Answers1