程式範例

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