Question

I have interface:

public interface CartService extends RemoteService{
    <T extends ActionResponse> T execute(Action<T> action);
}

I wish override ‘execute’ method in implementation:

public class XX implements CartService {

  @Override
  public <GetCartResponse> GetCartResponse execute(GetCart action) {
    // TODO Auto-generated method stub
    return null;
  }
}

But receive compiler error:
The method execute(GetCart) of type XX must override or implement a supertype method

GetCart & GetCartResponse:

public class GetCart implements Action<GetCartResponse>{

}


public class GetCartResponse implements ActionResponse {
    private final ArrayList<CartItemRow> items;

    public GetCartResponse(ArrayList<CartItemRow> items) {
        this.items = items;
    }

    public ArrayList<CartItemRow> getItems() {
        return items;
    }

}

How can I override this method ?

Answer 1

The problem is the definition of the interface vs what the erausre should look like for your impl. In your example you have:

<T extends ActionResponse> T execute(Action<T> action);
public <GetCartResponse> GetCartResponse execute(GetCart action);

but according to the interface definition the implementation method should read:

public GetCartResponse execute(Action<GetCartResponse> action);

So I think you either need to change the signature of your interface or add another type parameter such as:

public interface CartService extends RemoteService{
    <T extends ActionResponse, U extends Action> T execute(U action);
}

or possibly something along the lines of:

public interface CartService extends RemoteService{
    <T extends ActionItem> ActionResponse<T> execute(Action<T> action);
}