這種類型的引用在應用設計模式時非常適用(您可能需要通過面向對象設計的高級課程,或者從閱讀書籍開始:首先,設計模式,我建議)
請參閱例如如何在上述書中實現java中的裝飾器模式。
public abstract class Beverage {
String description = "Unknown Beverage";
public String getDescription() {
return description;
}
public abstract double cost();
}
則認爲我們有咖啡和在DarkRoast兩個子類:
public class Espresso extends Beverage {
public Espresso() {
this.description = "Espresso";
}
public double cost() {
return 1.99;
}
}
public class DarkRoast extends Beverage {
public DarkRoast() {
description = "Dark Roast Coffee";
}
public double cost() {
return .99;
}
}
現在
,我們要添加裝飾:
public abstract class CondimentDecorator extends Beverage {
public abstract String getDescription();
}
,並建立了一些具體的裝飾:
public class Mocha extends CondimentDecorator {
Beverage beverage;
public Mocha(Beverage beverage) {
this.beverage = beverage;
}
public String getDescription() {
return beverage.getDescription() + ", Mocha";
}
public double cost() {
return .20 + beverage.cost();
}
}
和另一包裝:
public class Whip extends CondimentDecorator {
Beverage beverage;
public Whip(Beverage beverage) {
this.beverage = beverage;
}
public String getDescription() {
return beverage.getDescription() + ", Whip";
}
public double cost() {
return .10 + beverage.cost();
}
}
終於,看到在主函數中發生了什麼,以及我們如何帶指針的優勢,以父類:
public static void main(String[] args) {
Beverage beverage = new Espresso();
System.out.println(beverage.getDescription() + " $" + beverage.cost());
Beverage beverage2 = new DarkRoast();
beverage2 = new Mocha(beverage2);
beverage2 = new Mocha(beverage2);
beverage2 = new Whip(beverage2);
System.out.println(beverage2.getDescription() + " $" + beverage2.cost());
你能猜到的輸出是什麼?以及:
Espresso $1.99
Dark Roast Coffee, Mocha, Mocha, Whip $1.49
你是什麼意思:**爲什麼我們需要分配給它,基類對象**你可以更清楚一點。 – 2012-03-23 05:26:27
@Rohit:在上面的例子中,當調用成員函數時,爲什麼當p本身是一個基類指針時,語句p =&b,爲什麼不直接使用它,如:p-> func()。我知道,我錯了,但我需要糾正它。 – user980411 2012-03-23 05:29:40