Question

Recently in an answer it was suggested to me that this:

public interface Operation<R extends OperationResult, P extends OperationParam> {

    public R execute(P param);
}

Is better than this:

public interface Operation {

    public OperationResult execute(OperationParam param);
}

I however can’t see any benefit in using the first code block over the second one …

Given that both OperationResult and OperationParam are interfaces an implementer needs to return a derived class anyway and this seems quite obvious to me.

So do you see any reason the use the first code block over the second one ?

Answer 1

This way you can declare your Operation implementations to return a more specific result, e.g.

 class SumOperation implements Operation<SumResult, SumParam>

Though whether this is of any value to your application depends entirely on the situation.

Update: Of course you could return a more specific result without having a generic interface, but this way you can restrict the input parameters as well.