这种类型的引用在应用设计模式时非常适用(您可能需要通过面向对象设计的高级课程,或者从阅读书籍开始:首先,设计模式,我建议)
请参阅例如如何在上述书中实现java中的装饰器模式。
public abstract class Beverage {
String description = "Unknown Beverage";
public String getDescription() {
return description;
}
public abstract double cost();
}
则认为我们有咖啡和在DarkRoast两个子类:
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;
}
}
现在
,我们要添加装饰:
public abstract class CondimentDecorator extends Beverage {
public abstract String getDescription();
}
,并建立了一些具体的装饰:
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();
}
}
和另一包装:
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();
}
}
终于,看到在主函数中发生了什么,以及我们如何带指针的优势,以父类:
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());
你能猜到的输出是什么?以及:
Espresso $1.99
Dark Roast Coffee, Mocha, Mocha, Whip $1.49
你是什么意思:**为什么我们需要分配给它,基类对象**你可以更清楚一点。 – 2012-03-23 05:26:27
@Rohit:在上面的例子中,当调用成员函数时,为什么当p本身是一个基类指针时,语句p =&b,为什么不直接使用它,如:p-> func()。我知道,我错了,但我需要纠正它。 – user980411 2012-03-23 05:29:40