Multiple inheritance on Java interfaces

Question

I thought multiple inheritance was always illegal in Java, but this code compiles:

public interface A {
  void a();
}

public interface B {
  void b();
}

pu         


        

Answer 1

Implementing interfaces is not "inheritance", which is when you extend a class.

Implementing interfaces is used to declare that a class "looks like" something, whereas extending classes is used to declare that a class "is a" something.

It's OK to "look like" multiple things, but not "be" multiple things.

There's nothing wrong with having empty interfaces that extend multiple interfaces as a way of collecting a set of interfaces into a single interface to convey a broader, but reused, API.