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。

类图

代码

Java

Client.java

package test21;

public class Client {

    public static void main(String[] args) {
        Observer observer = new PersonObserver();
        ConcreteSubject subject = new ConcreteSubject();

        subject.attach(observer);
        subject.setState("上涨");
        subject.notifyy();
        subject.setState("下跌");
        subject.notifyy();
    }

}

ConcreteSubject.java

package test21;

public class ConcreteSubject extends Subject{

    private String state;

    public void setState(String state) {
        this.state = state;
    }

    @Override
    public void notifyy() {
        if(state.equals("上涨")) {
            for (Object observer : observers) {
                ((Observer) observer).up_update();
            }
        }else if (state.equals("下跌")){
            for (Object observer : observers) {
                ((Observer) observer).down_update();
            }
        }
    }
}

Observer.java

package test21;

public interface Observer {

    public void up_update();
    public void down_update();

}

PersonObserver.java

package test21;

public class PersonObserver implements Observer{

    @Override
    public void up_update() {
        System.out.println("买股票");
    }

    @Override
    public void down_update() {
        System.out.println("大哭一场");
    }
}

Subject.java

package test21;

import java.util.ArrayList;

public abstract class Subject {

    protected ArrayList observers = new ArrayList();
    public void attach(Observer observer){
        observers.add(observer);
    }
    public void detach(Observer observer){
        observers.remove(observer);
    }
    public abstract void notifyy();

}

C++代码

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

//抽象观察者类
class Observer{
public:
    virtual void up_update(){}
    virtual void down_update(){}
};
//抽象物体类
class Subject{
protected:
    vector<Observer*> ob;
public:
    void attach(Observer *observer){
        ob.push_back(observer);
    }
    void detach(){
        ob.pop_back();
    }
    virtual void notify(){}
};
//具体观察者类
class PersonObserver: public Observer{
public:
    void up_update(){
        cout<<"股票上涨，开始买股票"<<endl;
    }
    void down_update(){
        cout<<"股票下跌，股民大哭"<<endl;
    }
};
//具体物体来
class ConcreteSubject: public Subject{
private:
    string state;
public:
    void setState(string state){
        this->state = state;
    }
    void notify(){
        for (int i=0; i<ob.size() ; i++) {
            if(state=="上涨")
                ob[i]->up_update();
            else
                ob[i]->down_update();
        }
    }
};

int main(){
    ConcreteSubject *subject = new ConcreteSubject();
    PersonObserver *observer = new PersonObserver();

    subject->attach(observer);
    subject->setState("上涨");
    subject->notify();
    subject->setState("下跌");
    subject->notify();
}