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
Novice
HP
MP
attack()
inheritance
inheritance
Magician
Swordman
magic_attack()
power_attack()
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
Novice
HP
MP
attack()
inheritance
Archer
attack()
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。
生物
Organism O = new Organism();
People P = new People();
Organism O2 = new People();
extends
動物
extends
人
•
Polymorphism
- Overriding
- Overloading
- Dynamic binding
- Interface/abstract
ArrayList
• ArrayList class that can be used to store an unlimited number
of objects.
Java.util.ArrayList
add(o object): void
add(index: int, o: object): void
clear(): void
indexOf(o: object): int
isEmpty(): boolean
lastIndexOf(o: object): int
remove(o: obect): boolean
size(): int
程式範例:
TestArrayList.java