1. Chapter 9 Interfaces and Polymorphism

2. 9.1 Reusing Code An interface is a collection of related methods whose headers are provided without implementation code. (abstraction) Methods are automatically public

3. Interfaces Provide a framework for behavior Classes which use the interface may have vastly different objects, but what they have in common is expressed in the interface

4. Example Interface FlyingObject Methods isFlying() fly() Example Classes: Bird, Airplane, Missile, Butterfly, Witch Non-Examples: Turtle

5. Example Interface Computable Methods add(), subtract(), multiply() Example Classes: Fraction, Matrix, LongInteger, ComplexNumber Non-Examples: TelevisionSet

6. Defining an Interface public interface InterfaceName { method headers }

7. Defining an Interface Example public interface FlyingObject { void fly(); boolean isFlying(); }

8. Implementing an Interface public class className implements InterfaceName, InterfaceName { methods fields }

9. Warning: Must define all methods of an interface if you want to use it.

10. UML FlyingObject > Witch

11. Implementing an Interface Example public class Witch implements FlyingObject { methods fields }

12. 9.2 Interface Types and Class Types It is legal to have a variable of an interface: FlyingObject x; However, x is NOT type FlyingObject Why not?

13. Witch wicked = new Witch(); FlyingObject y = wicked; //OK TelvisionSet tv = new TelevisionSet FlyingObject y = tv; //NOT OK Type of interface variable must be of a class which implements the interface

14. Casting Interfaces What if I needed to use another method from the Witch class that is NOT in the interface? Use a cast (Witch) y If you cast incorrectly, program will cause an error

15. 9.3 Polymorphism Polymorphic Methods: Methods which are overridden in more than one class Polymorphism: The ides that the type of object determines which form of the method is called

16. Overloaded vs. Polymorphic