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。

java实现

 

package observer;

import java.util.ArrayList;

public abstract class Subject {
    protected ArrayList<MyObserver> observers = new ArrayList<>();

    //注册
    public void attach(MyObserver obs){
        observers.add(obs);
    }
    //注销
    public void detach(MyObserver obs){
        observers.remove(obs);
    }
    //抽象改变
    public abstract void up(double a);

    public abstract void down(double a);
}

 

package observer;

public interface MyObserver {
    void responseUp();
    void responseDown();
}

package observer;
//股票，具体目标类
public class Stock extends Subject{
    @Override
    public void up(double a) {
        System.out.println("股票上涨"+(a*100)+"%");
        if(a>0.05){
            for (MyObserver observer : observers) {
                observer.responseUp();
            }
        }
    }

    @Override
    public void down(double a) {
        System.out.println("股票下跌"+(a*100)+"%");
        if(a>0){
            for (MyObserver observer : observers) {
                observer.responseDown();
            }
        }
    }
}

package observer;

public class StockHolder implements MyObserver{
    @Override
    public void responseUp() {
        System.out.println("股票上涨，买了一些股票");
    }

    @Override
    public void responseDown() {
        System.out.println("股票下跌，哭了");
    }
}

package observer;

public class Client {
    public static void main(String[] args) {
        Subject s = new Stock();
        StockHolder h1 = new StockHolder();
        s.attach(h1);
        s.up(0.06);
        System.out.println("-------------------");
        s.down(0.06);
    }
}

c++实现

// Created by 贾梓钊
#include<iostream>
#include<list>

using namespace std;

class MyObserver { ;;
public:
    virtual void responseUp(){}

    virtual void responseDown(){}
};

class MySubject{
protected:
    list<MyObserver*> obs;
public:
    void attach(MyObserver *ob){
        obs.push_back(ob);
    }
    void detach(MyObserver *ob){
        obs.remove(ob);
    }
    virtual void up(double a)=0;
    virtual void down(double a)=0;
};

class StockHolder:public MyObserver{
public:
    void responseUp(){
        cout<<"股票上涨，购买一些股票"<<endl;
    }
    void responseDown(){
        cout<<"股票下跌，大哭一场"<<endl;
    }
};

class Stock:public MySubject{
public:
    void up(double a){
        cout<<"股票上涨"<<(a*100)<<"%"<<endl;
        list<MyObserver*>::iterator iter=obs.begin();
        if(a>0.05){
            for(;iter!=obs.end();iter++){
                (*iter)->responseUp();
            }
        }
    }

    void down(double a){
        cout<<"股票下跌"<<(a*100)<<"%"<<endl;
        list<MyObserver*>::iterator iter=obs.begin();
        if(a>0.05){
            for(;iter!=obs.end();iter++){
                (*iter)->responseDown();
            }
        }
    }
};

int main(){
    MySubject *subject = new Stock();
    MyObserver *mo=new StockHolder();
    subject->attach(mo);
    subject->up(0.06);
    cout<<"----------------------"<<endl;
    subject->down(0.07);
    return 0;
}