一、前言：
- 观察者模式还有一个名字叫发布-订阅模式，我们熟悉的消息队列如ActiveMQ，就是采用的这种设计模式，
- 总的来说观察者模式主要难理解的地方有两个，一个是发布者对一个或多个观察者的管理，另一个就是实现消息发布者和订阅者之间的解耦。
二、观察者模式：
2.1、UML 图：
2.2、代码实例：
Step 1) 创建 Obser 接口：
public interface Obser {
public void updata(float temperature, float pressure, float humidity);
}
Step 2) 创建 CurrentConditions 实现类：
public class CurrentConditions implements Obser {
private float temperature;
private float pressure;
private float humidity;
public void updata(float temperature, float pressure, float humidity){
this.temperature = temperature;
this.pressure = pressure;
this.humidity = humidity;
display();
}
public void display(){
System.out.println("*** Taday Temperature：" + temperature + "***");
System.out.println("*** Taday Pressure：" + pressure + "***");
System.out.println("*** Taday Humidity：" + humidity + "***");
}
}
Step 3) 创建 BaiduSite 抽象类：
public class BaiduSite implements Obser{
private float temperature;
private float pressure;
private float humidity;
public void updata(float temperature, float pressure, float humidity){
this.temperature = temperature;
this.pressure = pressure;
this.humidity = humidity;
display();
}
public void display(){
System.out.println("*** 百度网站 Temperature：" + temperature + "***");
System.out.println("*** 百度网站 Pressure：" + pressure + "***");
System.out.println("*** 百度网站 Humidity：" + humidity + "***");
}
}
Step 4) 创建 SinaSite 实现类：
public class SinaSite implements Obser{
private float temperature;
private float pressure;
private float humidity;
public void updata(float temperature, float pressure, float humidity){
this.temperature = temperature;
this.pressure = pressure;
this.humidity = humidity;
display();
}
public void display(){
System.out.println("*** Sina Temperature：" + temperature + "***");
System.out.println("*** Sina Pressure：" + pressure + "***");
System.out.println("*** Sina Humidity：" + humidity + "***");
}
}
Step 5) 创建 Subject 接口：
public interface Subject {
public void registerObserver(Obser o);
public void removeObserver(Obser o);
public void notifyObservers();
}
Step 6) 创建 WeatherData 实现类：
public class WeatherData implements Subject {
private float temperature;
private float pressure;
private float humidity;
private ArrayList<Obser> obsers;
public WeatherData() {
obsers = new ArrayList<>();
}
public float getTemperature() {
return temperature;
}
public float getPressure() {
return pressure;
}
public float getHumidity() {
return humidity;
}
public void dataChange(){
notifyObservers();
}
public void setData(float temperature, float pressure, float humidity) {
this.temperature = temperature;
this.pressure = pressure;
this.humidity = humidity;
dataChange();
}
@Override
public void registerObserver(Obser o) {
obsers.add(o);
}
@Override
public void removeObserver(Obser o) {
if(obsers.contains(o)){
obsers.remove(o);
}
}
@Override
public void notifyObservers() {
for(int i=0; i<obsers.size(); i++){
obsers.get(i).updata(this.temperature, this.pressure, this.humidity);
}
}
}
Step 7) 创建 main 方法：
public class Client {
public static void main(String[] args) {
WeatherData weatherData = new WeatherData();
CurrentConditions currentConditions = new CurrentConditions();
BaiduSite baiduSite = new BaiduSite();
SinaSite sinaSite = new SinaSite();
weatherData.registerObserver(currentConditions);
weatherData.registerObserver(baiduSite);
weatherData.registerObserver(sinaSite);
System.out.println("通知各个注册的观察着，查看信息");
weatherData.setData(10f, 100f, 30.3f);
}
}
• 由 ChiKong_Tam 写于 2020 年 10 月 21 日