JAVA設計模式---裝飾者模式

寫在前面的話：

　　該模式動態的將責任附加到對象上，若要擴展功能，裝飾者提供了比繼承更有彈性的替代方案。裝飾者能夠在被裝飾者的行爲前面與/或後面加上本身的行爲，甚至將被裝飾者的行爲整個取代掉，而達到特定的目的。

　　該模式的實現意味着一羣裝飾者類，這些類反映出被裝飾的組件類型，用來包裝具體組件。

      缺點在於，能夠用無數個裝飾者包裝一個組件，但會致使設計中出現許多小對象，若是過分引用，會讓程序變得很複雜。

案例分析：

需求：模擬 StarbuzzCoffee 的訂單系統，咖啡原種類爲Espresso,HouseBlend，添加調料種類分別爲Soy,Mocha,Whip,對應不一樣的收費，杯子分爲大中小三種，分別對應不一樣的收費

代碼實現：

1）咖啡部分：

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

    public String getDescription(){
        return description;
    }

    public abstract double cost();
}
public class Espresso extends Beverage {
    public Espresso() {
        description = "Espresso";
    }

    @Override
    public double cost() {
        return 1.99;
    }
}

public class HouseBlend extends Beverage {
    public HouseBlend() {
        description = "HouseBlend";
    }

    @Override
    public double cost() {
        return 0.89;
    }
}

 

2）調料部分：

public abstract class CondimentBeverage extends Beverage {
    public abstract String getDescription();
}

public class Soy extends CondimentBeverage {
    Beverage beverage;

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

    @Override
    public String getDescription() {
        return beverage.getDescription();
    }

    @Override
    public double cost() {
        return 0.30+beverage.cost();
    }
}

public class Mocha extends CondimentBeverage {
    Beverage beverage;

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

    @Override
    public String getDescription() {
        return beverage.getDescription();
    }

    @Override
    public double cost() {
        return 0.20+beverage.cost();
    }
}

public class Whip extends CondimentBeverage {
    Beverage beverage;

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

    @Override
    public String getDescription() {
        return beverage.getDescription();
    }

    @Override
    public double cost() {
        return 0.40+beverage.cost();
    }
}

　3) 杯子選擇：

public abstract class Size extends Beverage {
    public abstract String getDescription();
}

public class BigSize extends Size {
    Beverage beverage;

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

    @Override
    public String getDescription() {
        return beverage.getDescription();
    }

    @Override
    public double cost() {
        return 0.30+beverage.cost();
    }
}

public class MiddleSize extends Size {
    Beverage beverage;

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

    @Override
    public String getDescription() {
        return beverage.getDescription();
    }

    @Override
    public double cost() {
        return 0.20+beverage.cost();
    }
}

public class SmalleSize extends Size {
    Beverage beverage;

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

    @Override
    public String getDescription() {
        return beverage.getDescription();
    }

    @Override
    public double cost() {
        return 0.10+beverage.cost();
    }
}

　4）測試代碼---生產訂單：

public class StarbuzzCoffee {
    public static void main(String[] args) {
        Beverage beverage1 = new Espresso();   //訂一杯Espresso，不添加任何調料
        System.out.println(beverage1.getDescription()+":$"+beverage1.cost());

        Beverage beverage2 = new HouseBlend();   //訂一杯HouseBlend，不添加任何調料
        beverage2 = new Mocha(beverage2);
        beverage2 = new Mocha(beverage2);   //兩份摩卡
        System.out.println(beverage2.getDescription()+"(double Mocha):$"+beverage2.cost());

        beverage2 = new Soy(beverage2);     //再加一份soy
        System.out.println(beverage2.getDescription()+"(additional Soy):$"+beverage2.cost());

        beverage2 = new Whip(beverage2);     //再加一份whip
        System.out.println(beverage2.getDescription()+"(additional Whip):$"+beverage2.cost());

        beverage2 = new MiddleSize(beverage2);   //選擇中杯
        System.out.println(beverage2.getDescription()+"(choose middleSize):$"+beverage2.cost());
    }
}

　測試結果：

Espresso:$1.99HouseBlend(double Mocha):$1.29HouseBlend(additional Soy):$1.59HouseBlend(additional Whip):$1.99HouseBlend(choose middleSize):$2.19