CSE115: Introduction to Computer Science I Dr. Carl Alphonce 219 Bell Hall

Announcements Exam 2 – 1 week away –covers material from exam 1 up to & including 10/15 –review on Monday 10/18 –exam on Wednesday 10/20

Agenda –interfaces and realization –type hierarchy

Interfaces and Realization form of interface definition function of an interface realization (“implements”) relationship

Form of an interface header + body –header access control modifier keyword ‘interface’ name (generally an adjective, following class name conventions, but prefixed with an upper- case ‘ I ’) –body method specifications (method headers followed by ‘;’, also called method declarations, as opposed to method definition)

Example public interface ICollarable { public void addCollar(Collar collar); public Collar removeCollar(); }

Example public class Dog implements ICollarable { private Collar _collar; public Dog(Collar collar) { _collar = collar; } public void setCollar(Collar collar) { _collar = collar; } public Collar removeCollar() { Collar temp = _collar; _collar = null; return temp; }

Example public class Dog implements ICollarable { private Collar _collar; public Dog(Collar collar) { _collar = collar; } public void addCollar(Collar collar) { _collar = collar; } public Collar removeCollar() { Collar temp = _collar; _collar = null; return temp; }

Example ICollarable x; x = new ICollarable(); NO! Cannot instantiate. x = new Dog(); OK if Dog implements ICollarable x = new Cat(); OK if Cat implements ICollarable

Calling methods ICollarable x; x = new ICollarable(); NO! Cannot instantiate. x = new Dog(); OK if Dog implements ICollarable x = new Cat(); OK if Cat implements ICollarable x.addCollar(new Collar()); OK x.removeCollar(); OK x.walk(); NO! Not all ICollarable objects define this method!

Demo in Eclipse

State systems State-based system: –system’s behavior based on its current state Many systems are state-based: –Cable/Satellite TV box –Wrist-watch –Cell phone interface

State Diagram OFFON push button

State Pattern example

Polymorphism Behavior determined by method of object, because… it’s the object that responds: –the type of the object determines response –the type of the reference to object doesn’t

Polymorphism declared type of variable a supertype of actual type of object

Proxy Pattern Polymorphism

Polymorphism (in proxy pattern) context delegates method call to concrete tool

State Pattern delegation

Delegation in State code public class DeskLamp { private IState _state; public DeskLamp() { _state = new Off(); } public void pushButton() { _state.pushButton(this); } public void setState(IState s) { _state = s; }

Proxy Pattern delegation

Delegation in Proxy code public class Proxy implements ISomething { private ISomthing _target; public Proxy(ISomething t) { _target = t; } public void methodA(X x, Y y, Z z) { _target.methodA(x, y, z); } public void methodB(R r, S s) { _target.methodB(r, s); } // and so on }