3、装饰者模式

public abstract class Beverage {
    public String describe = "没有描述信息！";
    public String getDescribe() {
        return describe;
    }

    public abstract double getCost();
}

public class EspressoBeverage extends Beverage {

    public EspressoBeverage(String describe) {
        this.describe = describe;
    }

    @Override
    public double getCost() {
        return 1.9;
    }
}

public class MochaBeverage extends Beverage {
    private Beverage beverage;

    public MochaBeverage(Beverage beverage) {
        this.beverage = beverage;
    }

    @Override
    public String getDescribe() {
        return beverage.getDescribe() + "，摩卡";
    }
    @Override
    public double getCost() {
        return beverage.getCost() + 2.0;
    }
}

public class MilkBeverage extends Beverage {
    private Beverage beverage;

    public MilkBeverage(Beverage beverage) {
        this.beverage = beverage;
    }

    @Override
    public String getDescribe() {
        return beverage.getDescribe() + "，加奶";
    }
    @Override
    public double getCost() {
        return beverage.getCost() + 0.3;
    }
}

public class Test {
    public static void main(String[] args) {
        Beverage espressoBeverage = new EspressoBeverage("正常咖啡");
        Beverage mochaBeverage = new MochaBeverage(espressoBeverage);
        Beverage milkBeverage = new MilkBeverage(mochaBeverage);

        System.out.println(mochaBeverage.getDescribe());
        System.out.println(mochaBeverage.getCost());
        System.out.println(milkBeverage.getDescribe());
        System.out.println(milkBeverage.getCost());
    }
}
执行结果：
正常咖啡，摩卡
3.9
正常咖啡，摩卡，加奶
4.2