Implementing a Generic Interface In Java

Question

I am new to Java Generics. I have to implement an interface which is of generic type. The syntax is as follows:

public interface A{}

public interface B<T extends A>{
    public T methodB(T a) ;
}

Now I have to implement B so Lets say my Class is C

public class C implements B<T extends A>{}

The java compiler is not letting me use it this way. Also I do not want to use raw types. Please help.

Eran · Accepted Answer · 2015-05-06 09:15:07Z

8

It should be

public class C<T extends A> implements B<T>

The type parameter is declared following the class name, and later can be used in the implements clause.

answered May 6, 2015 at 9:15

Eran

395k57 gold badges726 silver badges793 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

davioooh · Accepted Answer · 2015-05-06 11:08:16Z

3

If your implementing class is still a generic type you have to use this syntax:

public class C<T extends A> implements B<T> {}

As explained by Eran.

If C is not generic you simply need to specify the type argument for your interface:

public class C implements B<TypeExtendingA> {}

Where TypeExtendingA implements or extends A (or is A)

answered May 6, 2015 at 9:23

davioooh

24.8k47 gold badges172 silver badges262 bronze badges

But will it not limit the scope?

It depends on what you actually need. If you need to have a generic implementation go for the first option...