A good answer might be:

Yes.

Additional Facts about Interfaces

There are features of interfaces that the example did not show: A class can implement several interfaces:

class SomeClass extends SomeParent 
    implements InterfaceA, InterfaceB, InterfaceC
{

}

Now SomeClass must implement all the methods listed in all the interfaces.

QUESTION 20:

Could the interfaces contain several definitions of the same constant?