CSE115: Introduction to Computer Science I Dr. Carl Alphonce 219 Bell Hall Office hours: M-F 11:00-11:

Announcements Install session tonight: –Baldy 5:00 PM Exam 2 on Wednesday 10/21 –covers material from last exam up to and including Friday 10/16 Review on Monday 10/19

Recall the Dog class public class Dog { 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; }

Consider this code (assume association via constructor) Dog fido = new Dog(new Collar()); Dog rover = new Dog(new Collar()); fido rover _collar

Dog fido = new Dog(new Collar()); Dog rover = new Dog(new Collar()); fido.setCollar(rover.removeCollar()); public Collar removeCollar() { Collar temp = _collar; _collar = null; return temp; } Consider this code (assume association via constructor) fido rover temp _collar

Dog fido = new Dog(new Collar()); Dog rover = new Dog(new Collar()); fido.setCollar(rover.removeCollar()); public Collar removeCollar() { Collar temp = _collar; _collar = null; return temp; } Consider this code (assume association via constructor) fido rover temp _collar What happens here? Which _collar are we referring to here?

I left you with this puzzle to think about…

fido.setCollar(rover.removeCollar()); public Collar removeCollar() { Collar temp = _collar; _collar = null; return temp; } this fido rover this temp _collar What happens here? Which _collar are we referring to here?

rover.setCollar(fido.removeCollar()); public Collar removeCollar() { Collar temp = _collar; _collar = null; return temp; } this fido rover this temp _collar What happens here? Which _collar are we referring to here?

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!