Question

Why do we use interfaces in Java?

Answer 1

Like a class, an interface can have methods and variables, but the methods declared in interface are by default abstract (only method signature, no body).

Interfaces specify what a class must do and not how. It is the blueprint of the class.

An Interface is about capabilities like a Player may be an interface and any class implementing Player must be able to (or must implement) move(). So it specifies a set of methods that the class has to implement.

If a class implements an interface and does not provide method bodies for all functions specified in the interface, then class must be declared abstract.