C++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();
}

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