動態地給一個對象添加一些額外的職責。就增加功能來說，Decorator模式相比生成子類更為靈活。
例子：
被裝飾的接口：
public interface Cake {
public float cost();
}
接口的實現類：
public class MilkCake implements Cake{
@Override
public float cost() {
return 100f;
}
}
裝飾者抽象類：
public abstract class CakeDecorator implements Cake{
}
裝飾者的實現類
public class Chocolate extends CakeDecorator{
private Cake cake;
public Chocolate(Cake cake) {
this.cake = cake;
}
@Override
public float cost() {
float chocolatePrice = 25f;
return cake.cost() + chocolatePrice;
}
}
public class Berry extends CakeDecorator {
private Cake cake;
public Berry(Cake cake) {
this.cake = cake;
}
@Override
public float cost() {
float berryPrice = 5f;
return cake.cost() + berryPrice;
}
}
測試類：
public class Test {
public static void main(String[] args) {
MilkCake mc = new MilkCake();//牛奶蛋糕
System.out.println(mc.cost());
Berry b = new Berry(mc);//牛奶草莓蛋糕
System.out.println(b.cost());
Chocolate c = new Chocolate(b);//牛奶草莓巧克力蛋糕
System.out.println("付款:" + c.cost());
}
}