An Interface with Abstract Methods

Question

I came across some PHP code that was written by a co-worker (it was not used for anything). Basically it was an interface containing abstract methods. I then said that this was

Answer 1

All methods in an interface are abstract by definition.

An abstract method is a method for which the prototype is supplied but not implemented. It forces subclasses to implement it, or be declared abstract.

Answer 2

No, it's not useful. He should either use abstract classes or just plain interfaces.

Interface methods are basically abstract anyway, so having abstract interface methods doesn't make much sense.