实验 21：观察者模式

实验 21：观察者模式

[实验任务一]：股票提醒

当股票的价格上涨或下降5%时，会通知持有该股票的股民，当股民听到价格上涨的消息时会买股票，当价格下降时会大哭一场。

1. 类图：

 

 

2. 源代码：

#include <iostream>

#include <list>

using namespace std;

 

// 观察者接口

class IObserver {

public:

    virtual void respond(int rate) = 0;

};

 

// 主题接口

class ISubject {

protected:

    list<IObserver*> observers; // 存储观察者列表

public:

    // 注册方法

    void attach(IObserver* observer) {

        observers.push_back(observer);

    }

    // 注销方法

    void detach(IObserver* observer) {

        observers.remove(observer);

    }

    // 抽象通知方法

    virtual void notify(int rate) = 0;

};

 

// 具体主题类

class Stock : public ISubject {

public:

    void notify(int rate) override {

        for (auto observer : observers) {

            observer->respond(rate);

        }

    }

};

 

// 具体观察者类

class Holder : public IObserver {

public:

    void respond(int rate) override {

        if (rate >= 5) {

            cout << "股票上涨，购买股票" << endl;

        }

        else if (rate <= -5) {

            cout << "股票下跌，大哭一场" << endl;

        }

        else {

            cout << "股票还比较稳定哦~" << endl;

        }

    }

};

 

int main() {

    ISubject* subject = new Stock();

    IObserver* observer = new Holder();

    subject->attach(observer);

 

    cout << "----------------------股票上涨-----------------------" << endl;

    subject->notify(5);

    cout << endl;

 

    cout << "----------------------股票下跌-----------------------" << endl;

    subject->notify(-5);

    cout << endl;

 

    cout << "----------------------股票稳定-----------------------" << endl;

    subject->notify(4);

    cout << endl;

 

    delete observer;

    delete subject;

    return 0;

}

 运行截图：

 

3. 注意编程规范。