设计模式之装饰模式(Decorator)

装饰模式是一种经典的类功能扩展模式，其精髓在装饰类使用继承加聚合的方式获得接口和要实现对象，然后通过自己实现扩展接口

作用

装饰模式通过装饰类动态地将责任附加到对象上，若要扩展功能，无需通过继承增加子类就能扩展对象的新功能，提供了比继承更有弹性的替代方案，避免了子类数量膨胀带来的系统臃肿。

类视图

代码实现

class Component
{
public:
	Component(){}
	virtual ~Component(){}

	virtual void operation() = 0;
};


class ConcreteComponentA : public Component
{
public:
	ConcreteComponentA(){}
	~ConcreteComponentA(){}

	void operation()
	{
		fprintf(stderr, "ConcreteComponentA's operation!\n");
	}
};

class ConcreteComponentB : public Component
{
public:
	ConcreteComponentB(){}
	~ConcreteComponentB(){}

	void operation()
	{
		fprintf(stderr, "ConcreteComponentB's operation!\n");
	}
};

class Decorator : public Component
{
public:
	Decorator() :mComponent(NULL){}
	virtual ~Decorator(){}

	virtual void operation()
	{
		if (mComponent)
			mComponent->operation();
	}
	virtual void setComponent(Component* pComponent)
	{
		mComponent = pComponent;
	}

protected:
	Component* mComponent;
};


class ConcreteDecoratorE : public Decorator
{
public:
	ConcreteDecoratorE ();
	virtual ~ConcreteDecoratorE ();

	virtual void addBehavior()
	{
		mComponent->operation();
		fprintf(stderr, "ConcreteDecoratorE's addBehavior!\n");
	}
};

class ConcreteDecoratorF : public Decorator
{
public:
	ConcreteDecoratorF ();
	virtual ~ConcreteDecoratorF ();

	virtual void addBehavior()
	{
		operation();
		fprintf(stderr, "ConcreteDecoratorF's addBehavior!\n");
	}
};



int main()
{
	ConcreteComponentB *pComponent = new ConcreteComponentB();
	ConcreteDecoratorF decorator;
	decorator.setComponent(pComponent);
	decorator.addBehavior();
}