Two interfaces with same method signature implemented in Java class

Question

I have two Java interfaces and one implementing class.

(I have used Eclipse to run the program directly, and I did not try to check any compiler warning et cetera by

Answer 1

For this issue it's necessary to understand what interfaces are for.

An interface is a kind of "contract" so that one knows which methods are compulsorily implemented in a Class with that interface.

So if you need a Class implementing "DVDPlayer" (because you need the method "play()"), you'll find CarPlayer. Same goes for the need of a Class implementing CassettePlayer. That's the technical explanation.

But of course in your semantic coding you should ensure that CarPlayer's method "play()" satisfies the semantics of both DVDPlayer and CassettePlayer. I think in a practical application it will be a bad practice.

Of course in your example it's a bad idea to have two interfaces declaring the same method. More practically, you should have made an interface "Player" with method "play()" and have two other, more specific interfaces DVDPlayer and CassettePlayer (with specific methods for DVDs and cassettes) who inherit from Player. On the onther hand, if you don't need specific methods for DVDs or cassettes, then you don't need two different interfaces only implementing one and the same method - just use one interface Player, that'll be enough.