Interfaces and Packages

What it we really do need multiple inheritance?

Is a special kind of class which defines a specification of a set of methods. Provides a guarantee that any class that implements this interface will provide these methods. Is similar to setting «standards» and any class implementing it will get a «stamp of approval».

Interfaces are different from inheritance since interfaces do not inherit state or behavior, instead they just define a specification.

interface interfaceName {
     /* Method specifications */
}

class className implements interfaceName {
     /* Bodies for the interface methods */
     /* Own data and methods. */
}

interface MovableObject {
   boolean start();
   void stop();
   boolean turn(int degrees);
   double fuelRemaining();
   boolean changeSpeed(double kmPerHour);
}

class Plane implements MovableObject {
    boolean start() {
    //Do what's necessary to start the plane. Return true if it actually started.
    }
    void stop() {
    //Do whatever is necessary to stop the plane.
    }
    boolean turn(int degrees) {
    // Do what's necessary to turn the plane. Return true if it worked.
    }
    double fuelRemaining() {
    //Return the amount of plane fuel remaining.
    }
    boolean changeSpeed(double kmPerHour) {
    //Do what's necessary to accelerate or decelerate by the given amount
    }
}

In Java package is a collection of classes. May or may not be related by inheritance. Groups similar and interdependent classes together. The Java API is composed of multiple packages.

The import statement specifies particular classes, or an entire package of classes, that can be used in that program. Import statements are not necessary; a class can always be referenced by its fully qualified name in-line. If two classes from two packages have the same name and are used in the same program, they must be referenced by their fully qualified name.