装饰(decorate)模式

public interface Beverage {
    public double cost();
}
public class HouseBlend implements Beverage{
    @Override
    public double cost() {
        return 1;
    }
}
public class DarkRoast implements Beverage{
    @Override
    public double cost() {
        return 1;
    }
}
public abstract class CondimentDecorator implements Beverage{
    protected Beverage beverage;
}
public class Mocha extends CondimentDecorator {

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

    @Override
    public double cost() {
        return 1 + beverage.cost();
    }
}
public class Milk extends CondimentDecorator {

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

    @Override
    public double cost() {
        return 1 + beverage.cost();
    }
}
public class StartbuzzCoffee {
    public static void main(String[] args) {
        Beverage beverage = new HouseBlend();
        beverage = new Mocha(beverage);
        beverage = new Milk(beverage);
        System.out.println(beverage.cost());
    }
}