大話設計模式學習筆記-裝飾模式(c++描述)

首先什麼是“策略模式”：動態地給一個對象添加一些額外的職責，就增加功能來說，裝飾模式比生成之類更為靈活。大話設計模式P48）

裝飾模式UML類圖：

1、其中Component類定義了一個對象接口，可以給這些對象動態添加職責

2、ConcreteComponent類定義了具體的對象，這些對象是被添加職責

3、Decorator類定義了裝飾類的接口，繼承於Component類，用於給對象添加職責

3、ConcreteDecorator類是裝飾類的具體對象，這些實現類可以額外添加自己的特性或者行為，來到給對象添加職責，靈活性比繼承要好。

代碼實現：

//Component
class Component {
public:
    virtual void Operation() = 0;
};
//ConcreteComponent
class ConcreteComponent : public Component {
public:
    void Operation() {
        //具體對象的操作
    }
};
//Decorator
class Decorator : public Component {
public:
    void SetComponent(Component *pc) {
        this->component = pc;
    }
    void Operation() {
        if (component) {
            component->Operation();
        }
    }
protected:
    Component *component;
};
//ConcretrDecoratorA
class ConcretrDecoratorA : public Decorator {
public:
    void Operation() {
        Decorator::Operation();
        addedState = "";
        cout << addedState;
    }
private:
    string addedState; //增添特性
};
//ConcretrDecoratorB
class ConcretrDecoratorB : public Decorator {
public:
    void Operation() {
        Decorator::Operation();
        AddedBehavior();
        //do A
    }
private:
    void AddedBehavior() {
        //do B
    } //增添行為
};

客戶端：

int main() {
    ConcreteComponent *pc = new ConcreteComponent();
    ConcretrDecoratorA *pda = new ConcretrDecoratorA();
    ConcretrDecoratorB * pdb = new ConcretrDecoratorB();
    pda->SetComponent(pc);
    pdb->SetComponent(pda);
    pdb->Operation();
    return 0;
}

下面以飲料添加輔料來實戰演練一下：

一杯普通的咖啡只要5元，添加奶泡1元），添加巧克力2元），添加方糖1.5元）.....

所以以飲料類作為對象接口，有各種飲料的具體對象咖啡、奶茶、牛奶等等），和各種輔料類裝飾類），有奶泡，巧克力等等....

飲料類：

//飲料類
class Beverage {
public:
    Beverage() {}
    Beverage(string n, double c) : name(n), cost(c) {}
    virtual void show() {
        cout << name;
    }
    virtual double GetCost() {
        return cost;
    }
protected:
    string name;
    double cost;
};
//咖啡飲料，具體實現類
class Coffee : public Beverage {
public:
    Coffee() : Beverage("咖啡", 5) {}
};
//奶茶飲料，具體實現類
class MilkTea : public Beverage {
public:
    MilkTea() : Beverage("奶茶", 6) {}
};

輔料類:

//裝飾類，輔料
class Decorator : public Beverage {
public:
    void SetComponent(shared_ptr<Beverage> b) {
        beverage = b;
    }
    void show() {
        if (beverage)   beverage->show();
    }
    double GetCost() {
        if (beverage)   return beverage->GetCost();
    }
protected:
    shared_ptr<Beverage> beverage;
};
//輔料類，奶泡
class MilkFoam : public Decorator {
public:
    void show() {
        Decorator::show();
        cout << " + " << "奶泡";
    }
    double GetCost() {
        return Decorator::GetCost() + 1;
    }
};
//輔料類，巧克力
class Chocolate : public Decorator {
public:
    void show() {
        Decorator::show();
        cout << " + " << "巧克力";
    }
    double GetCost() {
        return Decorator::GetCost() + 2;
    }
};
//輔料類，方糖
class Suger : public Decorator {
public:
    void show() {
        Decorator::show();
        cout << " + " << "方糖";
    }
    double GetCost() {
        return Decorator::GetCost() + 1.5;
    }
};

客戶端代碼：

int main() {
    cout << "我要咖啡加方糖" << std::endl;
    shared_ptr<Beverage> coffee(new Coffee());
    shared_ptr<Decorator> suger(new Suger());
    suger->SetComponent(coffee);
    suger->show();
    cout << "\n總價格： " << suger->GetCost() << std::endl;
    cout << "我要奶茶,加奶泡和巧克力" << std::endl;
    shared_ptr<Beverage> milktea(new MilkTea());
    shared_ptr<Decorator> milkfoam(new MilkFoam());
    shared_ptr<Decorator> chocolate(new Chocolate());
    milkfoam->SetComponent(milktea);
    chocolate->SetComponent(milkfoam);
    chocolate->show();
    cout << "\n總價格： " << chocolate->GetCost() << std::endl;
    return 0;
}

結果：

裝飾模式可以靈活地為對象增加職責，是開放-封閉原則的很好體現之一！

本文出自 “加和文的世界” 博客，請務必保留此出處http://xuyjun.blog.51cto.com/7470650/1304165