设计模式之装饰者模式

设计模式, 读书笔记

装饰者模式

定义

动态地将责任附加到对象上。若要扩展功能，装饰者提供了比继承更有弹性的替代方案。

类图

CasrL9.jpg

代码示例

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class Beverage {
public:
	virtual string getDescription() {
		return description;
	}

	virtual double cost() = 0;

protected:
	string description;
};

class CondimentDecorator :public Beverage {
public:
	virtual string getDescription() = 0;
};

class Espresso :public Beverage {
public:
	Espresso(){
		description = "Espresso";
	}

	double cost() {
		return 1.99;
	}
};

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

	double cost() {
		return 0.89;
	}
};

class Mocha :public CondimentDecorator {
private:
	Beverage* beverage;
public:
	Mocha(Beverage* b) :beverage(b) {

	}

	string getDescription() {
		return beverage->getDescription() + ",Mocha";
	}

	double cost() {
		return 0.2 + beverage->cost();
	}
};

class Whip :public CondimentDecorator {
private:
	Beverage* beverage;
public:
	Whip(Beverage* b) :beverage(b) {

	}

	string getDescription() {
		return beverage->getDescription() + ",Whip";
	}

	double cost() {
		return 0.5 + beverage->cost();
	}
};

理解

使用接口，装饰者和被装饰者继承同一个接口，装饰者拥有一个被装饰者，当调用方法时，装饰者先执行自己新增的部分，再调用被装饰者的方法，这样就实现了扩展功能。

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