设计模式之代理模式和状态模式

1,代理(Proxy)模式基本思想:代理类派生自一个基类,由平行地派生自同一个基类的一个或多个类提供实际的实现.
2,代理模式和状态模式的区别:代理模式只有一个实现类,而状态模式有多个.
3,代码

#include <iostream>
using namespace std;

class ProxyBase
{
public:
    virtual void f()=0;
    virtual void g()=0;
    virtual void h()=0;
    virtual ~ProxyBase(){}
};

class Implemention : public ProxyBase
{
public:
    void f(){ cout<<"Implemention.f()"<<endl; }
    void g(){ cout<<"Implemention.g()"<<endl; }
    void h(){ cout<<"Implemention.h()"<<endl; }
};

class Proxy : public ProxyBase
{
    //定义基类指针接收实现类
    ProxyBase* pB;
public:
    //构造实现类
    Proxy(){ pB=new Implemention; }
    ~Proxy(){ delete pB; }
    void f(){ pB->f(); }
    void g(){ pB->g(); }
    void h(){ pB->h(); }
};

int main()
{
    Proxy p;
    p.f();
    p.h();
    p.g();
    return 0;
}

4,

#include <iostream>
using namespace std;

class Creature
{
    bool isFrog;
public:
    Creature() : isFrog(true) {}
    void greet()
    {
        if(isFrog)
            cout<<"Frog"<<endl;
        else
            cout<<"Prince"<<endl;
    }
    void kiss(){ isFrog=false; }
};

int main()
{
    Creature cr;
    cr.greet();
    cr.kiss();
    cr.greet();
    return 0;
}

这段代码执行操作前,都必须检查bool变量isFrog.
改用代理模式编写.

#include <iostream>
using namespace std;
class State
{
public:
    virtual string response()=0;
};

class Frog : public State
{
    string response(){ return "Frog"; }
};

class Prince : public State
{
    string response(){ return "Prince"; }
};

class Creature
{
    //基类指针替代布尔变量
    State* pB;
public:
    Creature() : pB(new Frog) {}
    void greet()
    {
        cout<<pB->response()<<endl;
    }
    void kiss(){ pB=new Prince; }
};

int main()
{
    Creature cr;
    cr.greet();
    cr.kiss();
    cr.greet();
    return 0;
}