More on Classes & Arrays

More on Classes & Arrays Pepper With help from http://docs.oracle.com/javase/tutorial/java/IandI/super.html and http://www.cis.upenn.edu/~palsetia/java/Animal/index.shtml

Review - A Class Trace Exercise What's wrong with the following program? public class SomethingIsWrong { public static void main(String[] args) { Rectangle myRect; myRect.width = 40; myRect.height = 50; System.out.println ("myRect's area is " + myRect.area()); } } http://docs.oracle.com/javase/tutorial/java/javaOO/QandE/objects-questions.html

Class Extension Make sub-classes (put "extends " classname after class) http://home.adelphi.edu/~pe16132/csc171/notes/fangstuff/Wackadot.java • Can use the entire extended class • Can override methods • This is how we use Fang's game class • Can see all protected and public methods and variables

Class Extension - Super • Can choose to execute methods from the super class using super.methodname • http://docs.oracle.com/javase/tutorial/java/IandI/super.html

Dog Class + Special type of Dog • Seeing Eye Dog is a dog • Properties: In addition to being a dog with a name, isAwake and position states, it has a tracking code • Actions: In addition to being able to makeNoise, sleep and wake, it can get its trackingcode and sit to warn for a curb. Credit to: http://www.cis.upenn.edu/~palsetia/java/Animal/index.shtml

Dog Class + Special type of Dog public class SeeingEyeDog extends Dog { private String trackingCode; public SeeingEyeDog(String name, String trackingCode){ super(name); this.trackingCode = trackingCode; } public String getTrackingCode(){ return this.trackingCode;} public String sitForCurb(){ super.sit(); super.makeNoise();} } public class Dog { private String name; private Boolean isAwake; private String position; public Dog (String name){ this.name = name; this.isAwake = true; this.position = "standing"; } public String makeNoise(){ return "bark"; } public void sleep(){ this.isAwake = false;} public void wake(){ this.isAwake = true;} public void sit(){ this.position = "sit";} } Credit to: http://www.cis.upenn.edu/~palsetia/java/Animal/index.shtml

Extended Class Used by Driver SeeingEyeDog can be placed into Dog or SeeingEyeDog variable type When in Dog type, it cannot get the tracking code public class DogDriver{ public static void main(){ Dog pepperPet = new Dog("Olive"); Dog working1 = new SeeingEyeDog("Sarah","ABC"); SeeingEyeDog working2 = new SeeingEyeDog("Coco","ABCD"); System.out.println (pepperPet.makeNoise()); System.out.println (working1.makeNoise()); System.out.println (working2.getTrackingCode()); // System.out.println (working1.getTrackingCode()); wont work if (working1 instanceofSeeingEyeDog){ SeeingEyeDog temp = (SeeingEyeDog) working1; System.out.println(temp.getTrackingCode()); }}}

Player Extension Make one player Extend to different player types Example: http://home.adelphi.edu/~pe16132/csc171/notes.html

Extension Limits • Can only extend one class • A seeing Eye Dog is a dog, but it is also a trainable being • Use Interface of trainable beings • Both the super and subclass can have objects created. • Animals share methods and properties, but cannot exist without being a specific type of animal such as Dog or Cat. • Use abstract class of Animals

Abstract Classes Cannot create its own object Can contain abstract classes, which every extender must code - compiler complains if the lower class does not implement it. http://docs.oracle.com/javase/tutorial/java/IandI/abstract.html

Abstract Class and its extensions public abstract class Animal{ private String name; private Boolean isAwake; public Animal (String name){ this.name = name; this.isAwake = true; } public void sleep(){ this.isAwake = false;} public void wake(){ this.isAwake = true;} public abstract String eats(); } public class Fish extends Animal { private booleanisSwimming; public Fish(String name) { super(name); this.isSwimming = true; } public String eats(){ return "little fish and algae";} } public class Dog extends Animal { private String position; public Dog (String name){ super(name); this.position = "standing"; } public String makeNoise(){ return "bark"; } public void sit(){ this.position = "sit";} public String eats(){ return "Meat and whatever else I find";} }

Animal Driver uses Abstract Class public class AnimalDriver { public static void main(){ Animal[] myAnimals = new Animal[2]; myAnimals[0] = new SeeingEyeDog("Sarah","ABC"); myAnimals[1] = new Fish ("James"); System.out.println (myAnimals[0].eats()); System.out.println (myAnimals[1].eats()); if (myAnimals[0] instanceof SeeingEyeDog){ SeeingEyeDog temp = (SeeingEyeDog) myAnimals[0]; System.out.println(temp.getTrackingCode()); } } }

Interface • Can create a type that has only abstract methods, with no properties. • Basically a contract to implement interfaces • Contains method headers with no code below it. • Lower classes can implement many interfaces (but only extend one class) • Implementing an interface means you promise (and the compiler checks) that you will implement the methods listed. • For out pets, trainable could be an interface containing the methods sit and stand and stay. • http://docs.oracle.com/javase/tutorial/java/IandI/interfaceDef.html

Summary - Class Types • Extension: To have all properties and method of super class in the sub class • Add extends <classname> to the subclass • Can override methods inside a subclass • Cannot access anything private in the class • Use super to use superclass methods if overridden • Abstract: To hold common code you want to extend • Cannot be used to create instances • Can insist method names be implemented • Interface: To insist method names be implemented • Cannot be used to create instances • Cannot have properties • Cannot code methods, only their headers

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