观察者模式

package com.sample;
import java.util.List;
import java.util.ArrayList;
public class ObserverDemo {
    public static void main(String[] args) {
        Subject subject = new Subject();
        Observer observer = new Observer();
        subject.attach(observer);
        subject.notify("hello");
    }
}
class Subject {
    private List<Observer> observerList = new ArrayList<Observer>();
    public void attach(Observer observer) {
        observerList.add(observer);
        System.out.println("attached an observer");
    }
    public void detach(Observer observer) {
        observerList.remove(observer);
    }
    public void notify(String state) {
        for (Observer observer : observerList) {
            observer.update(state);
        }
    }
}
class Observer {
    public void update(String state) {
        System.out.println("state is: " + state);
    }
}

#ifndef _OBSERVER_H_
#define _OBSERVER_H_
#include <string>
#include <list>
using namespace std;
class Subject;
class Observer
{
    public:
        void update(string state);
};
class Subject
{
    public:
        void notify(string state);
        void attach(Observer*);
        void Detach(Observer*);
    private:
        list<Observer*> observerList;
}
#endif

#include <iostream>
#include <algorithm>

#include "observer.h"
void Observer::update(string state)
{
    cout<<"state is: "<<state<<endl;
}
void Subject::attach(Observer* pobs)
{
    this->observerList.push_back(pobs);
    cout<<"attach an observer\n";
}
void Subject::detach(Observer* pobs)
{
    list<Observer*>::iterator iter;
    iter = find(observerList.begin(), observerList.end(), pobs);
    if (iter != observerList.end())
    {
        observerList.erase(iter);
    }
    cout<<"detach an observer\n";
}
void Subject::notify(string state)
{
    list<Observer*>::iterator iter = this->observerList.begin();
    for (; iter != observerList.end(); iter++)
    {
        (*iter)->update(state);
    }
}
Subject::~Subject()
{
    list<Observer*>::iterator iter = this->observerList.begin();
    for (; iter != observerList.end(); iter++)
    {
        delete *iter;
    }
    observerList.clear();
}
int main(int argc, char** argv)
{
    Observer* p1 = new Observer();
    Observer* p2 = new Observer();
    Observer* p3 = new Observer();
    Subject* pSubject = new Subject();
    pSubject->attach(p1);
    pSubject->attach(p2);
    pSubject->attach(p3);
    pSubject->notify("hello");
    return 0;
}