装饰器模式动态地将责任附加到对象上。想要扩展功能，装饰器提供于继承有别的另一种选择
java类图
java代码
public abstract class Beverage {
protected String description =
"Beverage";
public String
getDescription() {
return description;
}
public abstract double cost();
}
public class DarkRoast extends Beverage {
public DarkRoast() {
description =
"Dark Roast Coffee";
}
@Override
public double cost() {
return 0.99;
}
}
public class Decaf extends Beverage {
public Decaf() {
description =
"Decaf Coffee";
}
@Override
public double cost() {
return 1.05;
}
}
public class Espresso extends Beverage {
public Espresso() {
description =
"Espresso Coffee";
}
@Override
public double cost() {
return 1.99;
}
}
public class HouseBlend extends Beverage {
public HouseBlend() {
description =
"House Blend Coffee";
}
@Override
public double cost() {
return 0.89;
}
}
public abstract class CondimentDecorator extends Beverage {
public abstract String
getDescription();
}
public class Milk extends CondimentDecorator {
private Beverage beverage;
public Milk(Beverage beverage) {
this.beverage = beverage;
}
@Override
public String
getDescription() {
return beverage.getDescription() +
" ,Milk";
}
@Override
public double cost() {
return beverage.cost() +
0.1;
}
}
public class Mocha extends CondimentDecorator {
private Beverage beverage;
public Mocha(Beverage beverage) {
this.beverage = beverage;
}
@Override
public String
getDescription() {
return beverage.getDescription() +
" ,Mocha";
}
@Override
public double cost() {
return beverage.cost() +
0.2;
}
}
public class Soy extends CondimentDecorator {
private Beverage beverage;
public Soy(Beverage beverage) {
this.beverage = beverage;
}
@Override
public String
getDescription() {
return beverage.getDescription() +
" ,Soy";
}
@Override
public double cost() {
return beverage.cost() +
0.15;
}
}
public class Whip extends CondimentDecorator {
private Beverage beverage;
public Whip(Beverage beverage) {
this.beverage = beverage;
}
@Override
public String
getDescription() {
return beverage.getDescription() +
" ,Whip";
}
@Override
public double cost() {
return beverage.cost() +
0.1;
}
}
public class Test {
public static void main(String[] args) {
new Test().test();
}
private void test() {
Beverage espresso =
new Espresso();
System.out.println(espresso.getDescription() +
" $" + espresso.cost());
Beverage darkRoast =
new DarkRoast();
darkRoast =
new Mocha(darkRoast);
darkRoast =
new Mocha(darkRoast);
darkRoast =
new Whip(darkRoast);
System.out.println(darkRoast.getDescription() +
" $" + darkRoast.cost());
Beverage houseBlend =
new HouseBlend();
houseBlend =
new Soy(houseBlend);
houseBlend =
new Mocha(houseBlend);
houseBlend =
new Whip(houseBlend);
System.out.println(houseBlend.getDescription() +
" $" + houseBlend.cost());
}
}
注：
装饰者模式意味着一群装饰者类，这些类用来包装具体组件。装饰者反映出被装饰者的类型（事实上，他们具有相同的类型，都经过接口或者继承实现）。装饰者可以在被装饰者的行为前面/或后面加上自己的行为，甚至将被装饰者的行为整个取代掉，而达到特定的目的。你可以用无数个装饰者包装一个组件。装饰者一般对组件的客户是透明的，除非客户程序依赖于组件的具体类型。装饰者会导致设计中出现许多小对象，如果过度使用，会让程序变得很复杂。
参考文章 Head First 设计模式
