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
