Java@Ch11. Inheritance and Polymorphism

2010.12.31

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

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

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

程式範例 :

DynamicBindingDemo.java

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