JAVA2013.03.06

OUTLINE Inheritance Superclasses and Subclasses Using super keyword Overiding Method Overiding vs. Overloading Dynamic Binding Polymorphism

[Sample code]

Novice.java 、 Magician.java 、 Swordman.java 、 Game.java

DynamicBindingDemo.java

INHERITANCE Object-oriented programming allows you to derive

new classes from existing classes. This is called inheritance.

SUPERCLASSES AND SUBCLASSES

HPMP

magic_attack() power_attack()

Novice

Magician Swordman

attack()

inheritance inheritance

程式範例 : NOVICE.JAVA/* Superclass */

public class Novice //Novice 類別{

//---state, attribute-----int HP = 100;int MP = 50;

//---constructor----------Novice(){}

//---behavior------void attack() // 代表 attack 行為的 method{

System.out.println("Attack!");}

}

程式範例 : MAGICIAN.JAVA/* subclass */

public class Magician extends Novice //Magician類別 繼承Person{

//---state, attribute-----

//---constructor----------Magician(){

this.HP = 100;this.MP = 250;

}

//---behavior------void magic_attack() //代表magic attack行為的method{

if(this.MP >=10){

this.MP -= 10;System.out.println("Magic Attack!");

}}

}

程式範例 : SWORDMAN.JAVA/* Subclass */

public class Swordman extends Novice // Swordman 類別{

//---state, attribute-----

//---constructor----------Swordman(){

this.HP = 300;this.MP = 50;

}

//---behavior------void power_attack() //代表 attack 行為的 method{

System.out.println("Power Attack!");}

}

程式範例 : GAME.JAVA/* Game */

public class Game{

public static void main(String[] args){

// Declair a Novice objectNovice player1 = new Novice();System.out.println("player1 -> HP:" + player1.HP + " MP:" + player1.MP);player1.attack();

// Declair a Magician objectMagician player2 = new Magician();System.out.println("player2 -> HP:" + player2.HP + " MP:" + player2.MP);player2.attack();player2.magic_attack();

// Declair a Swordman objectSwordman player3 = new Swordman();System.out.println("player3 -> HP:" + player3.HP + " MP:" + player3.MP);player3.attack();player3.power_attack();

// Declair a Archer objectArcher player4 = new Archer();System.out.println("player3 -> HP:" + player4.HP + " MP:" + player4.MP);player4.attack();

}}

USING SUPER KEYWORD• The super refers to the superclass of the class in which super

appears.

• It can be used in two ways:

1. To call a superclass constructor.

2. To call a superclass method.

OVERIDING METHOD

HPMP

Novice

attack()

attack()

Archer

inheritance

overriding

程式範例 : ARCHER.JAVA/* Subclass */

public class Archer extends Novice // Archer類別{

//---state, attribute-----

//---constructor----------Archer(){

this.HP = 200;this.MP = 150;

}

//---behavior------void attack() //代表attack行為的method, override the

Novice.attack(){

System.out.println("Shoot!");}

}

OVERIDING VS. OVERLOADING Overriding 覆寫

Sometimes it is necessary for the subclass to modify the

implementation of a method defined in the superclass.

Overloading 多載Define multiple methods with the same name but different

signature .

( 課本 p.407)

DYNAMIC BINDING Dynamic Binding 動態載入

物件的行為並不是在編譯時期 (compiler-time) 就已經決定了。而是在程式執行時期於 (run-time) 才動態地決定 的。如何動態地決定。就看物件當時的狀態(state) 而定，物件封裝了所有可能的狀態處理 方法，並且根據外邊送來的訊息做出適當的反應。

( 課本 p.409)

程式範例 : DYNAMICBINDINGDEMO.JAVA

public class DynamicBindingDemo{

public static void main(String [] args){

m(new GraduateStudent());m(new Student());m(new Person());m(new Object());

}public static void m(Object x){

System.out.println(x.toString());}

}

class GraduateStudent extends Student{}

class Student extends Person{

public String toString(){

return "Student";}

}

class Person{

public String toString(){

return "Person";}

}

POLYMORPHISM Polymorphism 多型

簡單來說，多型是指一個物件可以擁有多個不同的型態，而這些型態必須是該物件所繼承的其他類別。

Organism O = new Organism();

People P = new People();

Organism O2 = new People();

生物

動物

人

extends

extends

Polymorphism

- Overriding

- Overloading

- Dynamic binding

- Interface/abstract

ARRAYLIST ArrayList class that can be used to store an unlimited number

of objects.

add(o object): voidadd(index: int, o: object): voidclear(): voidindexOf(o: object): intisEmpty(): booleanlastIndexOf(o: object): intremove(o: obect): booleansize(): int

Java.util.ArrayList

程式範例 : TESTARRAYLIST.JAVA/* ArrayList */class Car{

int speed(){

return 100;}void run(){

System.out.println("Runing!");}

}

public class TestArrayList{

@SuppressWarnings("unchecked")public static void main(String[] args){

java.util.ArrayList cityList = new java.util.ArrayList();cityList.add("Taipei");cityList.add("Taichung");cityList.add("Kaushiung");

java.util.ArrayList list = new java.util.ArrayList();list.add(new Car());list.add(new Car());System.out.println(((Car)list.get(0)).speed());//System.out.println(((Car)list.get(1)).run());

}}

PRACTICE 1. (The Person, Student, Employee, Faculty,

and Staff classes) Design a class named Person and its two subclasses named Student and Employee. Make Faculty and Staff subclasses of Employee. A person has a name, address, phone number, and email address. A student has a class status (freshman, sophomore, junior, or senior). Define the status as a constant. An employee has an office, salary, and date hired. Define a class named MyDate that contains the fields year, month, and day. A faculty member has office hours and a rank. A staff member has a title. Override the toString method in each class to display the class name and the person’s name.

Ppt 下載： http://oss.csie.fju.edu.tw/~jastine01/

ppt.html