一、观察者设计模式能够解决什么问题呢？
当一个对象发生指定的动作时，要通过另外一个对象做出相应的处理。
二、观察者设计模式的步骤：
三、经典的天气预报
WeatherStation 类：
public class WeatherStation {
String [] weathers={"晴天","雾霭","下雨天"};
//当前天气
String weather;
//该集合中存储的是需要收听天气
ArrayList<Weather> list=new ArrayList<Weather>();
public void addListener(Weather e){
list.add(e);
}
//开始工作
public void startWork() throws Exception{
Random random=new Random();
while(true){
updateWeather();
for(Weather e:list){ //通知调用者
e.notifyWeather(weather);
}
int s=random.nextInt(501)+1000;
Thread.sleep(s);
}
}
public void updateWeather(){ //更新天气
Random random=new Random();
int index=random.nextInt(3);
weather=weathers[index];
System.out.println("当前天气为："+weather);
}
}
Weather 接口：
package observer;
public interface Weather {
//订阅天气预报
public void notifyWeather(String weather);
}
Student 类：
package observer;
public class Student implements Weather{
String name;
public Student(String name) {
this.name = name;
}
@Override
public void notifyWeather(String weather) {
if("雾霭".equals(weather)){
System.out.println("今天天气是"+weather+" "+name+"带着口罩去上学");
}else if("晴天".equals(weather)){
System.out.println("今天天气是"+weather+" "+name+"开开心心去上学");
}else{
System.out.println("今天天气是"+weather+" "+name+"在家休息");
}
}
}
测试类：
public class WeatherMain {
public static void main(String[] args) throws Exception {
Student student=new Student("小明");
Student student1=new Student("老王");
WeatherStation weatherStation=new WeatherStation();
weatherStation.addListener(student);
weatherStation.addListener(student1);
weatherStation.startWork();
}
}
原文：http://www.cnblogs.com/lyjs/p/5078050.html