Interface Inheritance

Interfaces

The interface keyword is for defining interfaces in class hierarchies. interface is very similar to class with the following restrictions:

• The member functions that it declares (but not implements) are abstract even without the abstract keyword.

• The member functions that it implements must be static or final. (static and final member functions are explained later in this chapter.)

• Its member variables must be static.

• Interfaces can inherit only interfaces.

Despite these restrictions, there is no limit on the number of interfaces that a class can inherit from. This is unlike classes where a class can inherit from up to one class only.

Definition

Interfaces are defined by the interface keyword, the same way as classes:

interface SoundEmitter {
    //....
}

An interface is for declaring member functions that are ...