[Structural Pattern] Understanding of Decorator Pattern

head File

//DecoratorPattern.h

#ifndef DECORATOR_PATTERN_H
#define DECORATOR_PATTERN_H

#include <Windows.h>
#include <iostream>
using namespace std;

namespace DecoratorPattern
{
    /*
    ** FileName     : DecoratorPatternDemo
    ** Author       : Jelly Young
    ** Date         : 2013/12/19
    ** Description  : More information, please go to http://www.jellythink.com
    */

    class Component
    {
    public:
        Component();
        virtual ~Component();
        virtual void Operation() = 0;
    };

    class ConcreteComponent : public Component
    {
    public:
        ConcreteComponent();
        virtual ~ConcreteComponent();
        virtual void Operation();
    };

    //
    //////////////////////////////////////////////////////////////////////////
    class Decorator : public Component
    {
    public:
        Decorator(Component* pComponent);
        virtual ~Decorator();
        virtual void Operation();

    protected:
        Component* m_pComponentObj;
    };

    class ConcreteDecoratorA : public Decorator
    {
    public:
        ConcreteDecoratorA(Component* pDecorator) ;
        virtual ~ConcreteDecoratorA();

        virtual void Operation();

        void  AddedBehavior();
    };

    class ConcreteDecoratorB : public Decorator
    {
    public:
        ConcreteDecoratorB(Component* pDecorator);
        virtual ~ConcreteDecoratorB();

        virtual void Operation();
        void  AddedBehavior();
    };

    //////////////////////////////////////////////////////////////////////////
    void DecoratorPattern_Test();
}

#endif

accomplish

#include "DecoratorPattern.h"

namespace DecoratorPattern
{
    Component::Component()
    {
    }

    Component::~Component()
    {
    }

    //
    //////////////////////////////////////////////////////////////////////////
    ConcreteComponent::ConcreteComponent()
    {
    }

    ConcreteComponent::~ConcreteComponent()
    {
    }

    void ConcreteComponent::Operation()
    {
        cout<<"I am no decoratored ConcreteComponent"<<endl;
    }
    

    //
    //////////////////////////////////////////////////////////////////////////
    Decorator::Decorator(Component *pComponent)
        : m_pComponentObj(pComponent)
    {}

    Decorator::~Decorator()
    {}

    void Decorator::Operation()
    {
        if (m_pComponentObj != NULL)
        {
            m_pComponentObj->Operation();
        }
    }

    //////////////////////////////////////////////////////////////////////////
    ConcreteDecoratorA::ConcreteDecoratorA(Component* pDecorator)
        : Decorator(pDecorator)
    {}

    ConcreteDecoratorA::~ConcreteDecoratorA()
    {}

    void ConcreteDecoratorA::Operation()
    {
        AddedBehavior ();
        Decorator::Operation();
    }
    void  ConcreteDecoratorA::AddedBehavior()
    {
        cout<<"This is added behavior A."<<endl;
    }

    ConcreteDecoratorB::ConcreteDecoratorB(Component *pDecorator)
        : Decorator(pDecorator)
    {}
    ConcreteDecoratorB::~ConcreteDecoratorB()
    {}
    void ConcreteDecoratorB::Operation()
    {
        AddedBehavior ();
        Decorator::Operation();
    }
    void ConcreteDecoratorB::AddedBehavior()
    {
        cout<<"This is added behavior B."<<endl;
    }


    //////////////////////////////////////////////////////////////////////////
    void DecoratorPattern_Test()
    {
        Component *pComponentObj = new ConcreteComponent();
        Decorator *pDecoratorAOjb = new ConcreteDecoratorA(pComponentObj);
        pDecoratorAOjb->Operation();
        cout<<"============================================="<<endl;
        Decorator *pDecoratorBOjb = new ConcreteDecoratorB(pComponentObj);
        pDecoratorBOjb->Operation();
        cout<<"============================================="<<endl;
        Decorator *pDecoratorBAOjb = new ConcreteDecoratorB(pDecoratorAOjb);
        pDecoratorBAOjb->Operation();
        cout<<"============================================="<<endl;

        delete pDecoratorBAOjb;
        pDecoratorBAOjb = NULL;
        delete pDecoratorBOjb;
        pDecoratorBOjb = NULL;
        delete pDecoratorAOjb;
        pDecoratorAOjb = NULL;
        delete pComponentObj;
        pComponentObj = NULL;
    }
}

client

#include "DecoratorPattern.h"


#include <iostream>
using namespace std;
using namespace DecoratorPattern;

void main()
{
    DecoratorPattern_Test();
}

operation result