软件设计21|观察者模式

一、Java版本

（1）效果如下：

（2）类图如下：

（3）工程目录如下：

（4）代码如下：

Client.java

package observer;

public class Client {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        
        ConcreteSubject subject=new ConcreteSubject();
        ConcreteObserver investor1=new ConcreteObserver("股民1");
        ConcreteObserver investor2=new ConcreteObserver("股民2");
        ConcreteObserver investor3=new ConcreteObserver("股民3");
        subject.add(investor1);
        subject.add(investor2);
        subject.add(investor3);
        
        subject.Rise(0.1);
        subject.Rise(0.001);
        
        subject.remove(investor3);
        System.out.println();
        
        subject.Down(0.1);
        subject.Down(0.001);
    }

}

ConcreteObserver.java

package observer;

//具体观察者
public class ConcreteObserver implements Observer {

    private String name;
    public ConcreteObserver(String name){
        this.setName(name);
    }
    
    @Override
    public void Rise() {
        // TODO Auto-generated method stub
        System.out.println("价格上涨,"+name+"买股票！");
    }

    @Override
    public void Down() {
        // TODO Auto-generated method stub
        System.out.println("价格下降,"+name+"大哭一场！");
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

}

ConcreteSubject.java

package observer;

import java.util.ArrayList;

//具体目标类
public class ConcreteSubject extends Subject {

    private ArrayList<Observer> observer;
    
    public ConcreteSubject() {
        observer=new ArrayList<>();
    }
    
    @Override
    public void add(Observer o) {
        // TODO Auto-generated method stub
        observer.add(o);
    }

    @Override
    public void remove(Observer o) {
        // TODO Auto-generated method stub
        observer.remove(o);
    }

    @Override
    public void Rise(double rise) {
        // TODO Auto-generated method stub
        if(rise>0.05) {
            for(Observer obs:observer) {
                obs.Rise();
            }
        }
    }

    @Override
    public void Down(double down) {
        // TODO Auto-generated method stub
        if(down<0.05) {
            for(Observer obs:observer) {
                obs.Down();
            }
        }
    }

}

Observer.java

package observer;

//抽象观察者
public interface Observer {
    public void Rise();//股票升
    public void Down();//股票降
}

Subject.java

package observer;

//抽象目标类
public abstract class Subject {
    public abstract void add(Observer observer);
    public abstract void remove(Observer observer);
    public abstract void Rise(double rise);
    public abstract void Down(double down);
}

（5）参考链接：设计模式——观察者模式

二、C++版本

（1）效果如下：

（2）类图如下：

（3）代码如下：

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

class Subject;
class Observer
{
public:
    Observer() {};
    virtual ~Observer() {};
    virtual void Rise() = 0;//股票上升
    virtual void Down() = 0;//股票下降
};

class ConcreteObserver :public Observer
{
public:
    ConcreteObserver(string name, Subject* subject) :m_observerName(name), m_subject(subject) {};
    ~ConcreteObserver() {};
    void Rise() {
        cout << "价格上涨," << m_observerName << "买股票！" << endl;
    }
    void Down() {
        cout << "价格下降," << m_observerName << "大哭一场！" << endl;
    }
private:
    string m_observerName;
    Subject* m_subject;
};

class Subject
{
public:
    Subject() {};
    virtual ~Subject() {};
    void addObserver(Observer* observer) {
        m_observers.push_back(observer);
    }
    void deleteObserver(Observer* observer) {
        for (vector<Observer*>::iterator iter = m_observers.begin();iter != m_observers.end(); iter++){
            if (*iter == observer){
                m_observers.erase(iter);
                return;
            }
        }
    }
    void Rise(double rise) {
        if(rise>0.05){
            for (vector<Observer*>::iterator iter = m_observers.begin();iter != m_observers.end();iter++){
                (*iter)->Rise();
            }
        }
    }
    void Down(double down) {
        if (down < 0.05) {
            for (vector<Observer*>::iterator iter = m_observers.begin(); iter != m_observers.end(); iter++) {
                (*iter)->Down();
            }
        }
    }
private:
    vector<Observer*> m_observers;
};

class ConcreteSubject :public Subject
{
public:
    ConcreteSubject(string name) :m_subjectName(name) {};
    ~ConcreteSubject() {};
private:
    string m_subjectName;
};

int main()
{
    Subject* subject = new ConcreteSubject("subject");

    Observer* observerA = new ConcreteObserver("observerA", subject);
    Observer* observerB = new ConcreteObserver("observerB", subject);

    subject->addObserver(observerA);
    subject->addObserver(observerB);

    subject->Rise(0.1);
    cout << "***" << endl;
    subject->Down(0.01);

    return 0;
}

（4）参考链接：设计模式-观察者模式 C++实现