How to implement interface method with generic

Question

public interface A {
  public void setStar(Star star)
}

public class A-Class implements A {
 public void setStar(StarImpl star)
}

public interface Star {
}

public class StarImpl implements Star {
}

So basically, I want to apply interface A to A-Class. But it gives me error: A-Class is not abstract and does not override abstract method setStar(Star).

I know the reason is that setStar() in A-class is not exact as the one in interface A. But I don't know how to use generic to fix it? Any ideas? Thanks you very much!

What I tried:

public class A-Class implements A {
 public void setStar(<? extends Star> star)
}

public class A-Class implements A {
 public <T extends Star> void setStar(T star)
}

Both of them doesn't work. Again, thanks in advance!

change name of A-Class. There is something wrong with your details. Error should be `A-Class is not abstract and does ..` — Ravi, Jan 19 '18 at 03:53
[What is PECS (Producer Extends Consumer Super)?](https://stackoverflow.com/q/2723397/2970947) — Elliott Frisch, Jan 19 '18 at 03:56
@ElliottFrisch Does it mean I need to change the interface into superclass? — Haoyu Chen, Jan 19 '18 at 05:04
Depends on what you're trying to do; read that link again. It tells you when you need `extends`, `super` or neither. You told us it doesn't work, not what you want it to do... — Elliott Frisch, Jan 19 '18 at 05:10
@ElliottFrisch Really appreciate for your quick response! Basically, I want to make the interface A used in two classes, where it needs to implement those method to accept two type of class (both of them are implemented from interface Star). — Haoyu Chen, Jan 19 '18 at 05:14
Then should not `Star` itself be generic? Please post a MCVE. I can't tell what you're asking. — Elliott Frisch, Jan 19 '18 at 05:19
Do you mean make the interface `Star` as generic? Is it possible for you to give an example? — Haoyu Chen, Jan 19 '18 at 05:22

score 0 · Accepted Answer · answered Jan 19 '18 at 05:38

0

public interface A<T extends Star> {
  public void setStar(T star)
}

After some trying, I solved the problem by myself. Basically, it's to add generic to interface A. Thanks, guys!

answered Jan 19 '18 at 05:38

Haoyu Chen

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How to implement interface method with generic

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