裝飾者模式簡單示例(一)

裝飾者模式

代碼執行個體參考于《HeadFirst設計模式》。

飲料的抽象類

public abstract class Beverage {
     String description = "Unknown beverage";

     public String getDescription(){
         return description;
     }
     // cost必須在子類中實作
     public abstract double cost();
}

           

調料的抽象類

public abstract class CondimentDecorator extends Beverage {
    // 子類重寫getDescription方法
    @Override
    public abstract String getDescription();
}

           

飲料具體子類

// 濃縮咖啡
public class Espresso extends Beverage {
    public Espresso() {
        description = "Espresso";
    }
    @Override
    public double cost() {
        return 1.99;
    }
}
// 綜合咖啡
public class HouseBlend extends Beverage {
    public HouseBlend() {
        description = "House Blend Coffee";
    }
    @Override
    public double cost() {
        return 0.89;
    }
}
// 深焙
public class DarkRoast extends Beverage {
    public DarkRoast() {
        description = "DarkRoast Coffee";
    }
    @Override
    public double cost() {
        return 0.99;
    }
}
           

調料具體子類

// 摩卡
public class Mocha extends CondimentDecorator {
    Beverage beverage;
    public Mocha (Beverage beverage){
        this.beverage = beverage;
    }
    @Override
    public String getDescription() {
        return beverage.getDescription() + ", Mocha";
    }
    @Override
    public double cost() {
        return 0.20 + beverage.cost();
    }
}
// 豆漿
public class Soy extends CondimentDecorator {
    Beverage beverage;
    public Soy(Beverage beverage) {
        this.beverage = beverage;
    }
    @Override
    public String getDescription() {
        return beverage.getDescription() + ", Soy";
    }
    @Override
    public double cost() {
        return 0.15 + beverage.cost();
    }
}
// 奶泡
public class Whip extends CondimentDecorator {
    Beverage beverage;
    public Whip(Beverage beverage) {
        this.beverage = beverage;
    }
    @Override
    public String getDescription() {
        return beverage.getDescription() + ", Whip";
    }
    @Override
    public double cost() {
        return 0.10 + beverage.cost();
    }
}
           

測試類

public class StarbuzzCoffee {
    public static void main(String args[]) {
        Beverage beverage = new Espresso();
        System.out.println(beverage.getDescription() + " $" + beverage.cost());

        Beverage beverage2 = new HouseBlend();
        beverage2 = new Soy(beverage2);
        beverage2 = new Mocha(beverage2);
        beverage2 = new Whip(beverage2);
        System.out.println(beverage2.getDescription() +" $"+ beverage2.cost());

        Beverage beverage3 = new DarkRoast();
        beverage3 = new Mocha(beverage3);
        beverage3 = new Mocha(beverage3);
        beverage3 = new Whip(beverage3);
        System.out.println(beverage3.getDescription() +" $"+ beverage3.cost());
    }
}
           

小結

我們這邊是利用繼承達到“類型”比對的目的，而不是利用繼承獲得行為。

行為來自裝飾者和基礎元件，或與其他裝飾者之間的組合關系。

裝飾者該做的事，就是增加行為到被包裝的對象上。

繼承鍊如下圖：