气象局系统：气象台能够经过物理装置获得气象新闻，WeatherData对象足以由此气象局提供的外表接口获取气象新闻。
要求：WeatherData获得最新数据时，供给实时更新七个公告板的情景数据。几个文告板分别是：近年来情景、气象总括、天气预测。
风度翩翩、收拾解析：
1.WeatherData有多个getter方法getTemperature()，getHumidity()，getPressure()分别获得温度、湿度、气压值；
2.当数码变动时，WeatherData有个措施measurementsChanged()会被调用(大家不关心什么被调用)，当时需改善八个公告板的景色消息；
3.系统需可扩张，可天天新添或然去除文告板。
率先次尝试：
1 public class WeatherData {
2
3 public void measurementsChanged() {
4 float temperature = getTemperature();
5 float humidity = getHumidity();
6 float pressure = getPressure();
7 //目前状况布告板更新
8 currentConditionsDisplay.update(temperature, humidity, pressure);
9 //气象统计布告板更新
10 statisticsDisplay.update(temperature, humidity, pressure);
11 //天气预报布告板更新
12 forecastDisplay.update(temperature, humidity, pressure);
13 }
14
15 //WeatherData的其他方法
16
17 }
存在的主题材料：针对贯彻编制程序，会难以扩展和护卫，如若须求新增添大概去除布告板，必得修改该程序。
比方说报社，订阅报纸后，报社会定时给你邮寄报纸，甘休订阅后报社便销声匿迹邮寄。大家把报社会改良称为“大旨Subject”，把订阅者改成为“观望者 Observer”来研商观看者格局。
旁观者情势定义：定义了目的之间的豆蔻梢头对多信赖，那样一来，当三个对象改变时，它的持有信任者都会摄取公告并自动更新。
lovebet下载，宗旨不须要理解观察者具体是何人，只需求明白阅览者完成了Observer接口，并不关怀阅览者具体做了什么样事，这种互动对象间的松耦合是安顿性中追求的条件，上面看宗旨Subject和观看者Observer接口代码：
1 /*观察者*/
2 public interface Observer {
3 public void update(float temp, float humidity, float pressure);
4 }
1 /*主题*/
2 public interface Subject {
3 /*注册成为观察者*/
4 public void registerObserver(Observer o);
5 /*移除观察者*/
6 public void removeObserver(Observer o);
7 /*通知所有观察者*/
8 public void notifyObservers();
9 }
1 public interface DisplayElement {
2 /**
3 * 布告板都实现该接口，调用display来展示气象信息
4 */
5 public void display();
6 }
前日让WeatherData达成宗旨接口：
1 public class WeatherData implements Subject {
2 private List<Observer> observerList;
3 private float temperature;
4 private float humidity;
5 private float pressure;
6
7 public WeatherData() {
8 observerList = new ArrayList<Observer>();
9 }
10 public void registerObserver(Observer o) {
11 observerList.add(o);
12 }
13
14 public void removeObserver(Observer o) {
15 int i = observerList.indexOf(o);
16 if (i >= 0) {
17 observerList.remove(i);
18 System.out.println(o.getClass().getName() + " is removed.");
19 }
20 }
21
22 public void notifyObservers() {
23 for (Observer o : observerList) {
24 o.update(temperature, humidity, pressure);
25 }
26 }
27 /*数据更新时，通知所有观察者*/
28 public void measurementsChanged() {
29 notifyObservers();
30 }
31
32 }
通告板达成观看者接口：
1 /*目前状况布告板*/
2 public class CurrentConditionsDisplay implements Observer, DisplayElement {
3
4 private float temperature;
5 private float humidity;
6 private Subject weatherData;
7
8 public CurrentConditionsDisplay(Subject subject) {
9 this.weatherData = subject;
10 weatherData.registerObserver(this);
11 }
12
13 public void removeObserver() {
14 weatherData.removeObserver(this);
15 }
16
17 public void update(float temp, float humidity, float pressure) {
18 this.temperature = temp;
19 this.humidity = humidity;
20 display();
21 }
22
23 public void display() {
24 System.out.println("CurrentConditionsDisplay conditions:" + temperature + "F degrees and " + humidity + "% humidity");
25 }
26
27 }
28
29 /*天气预报布告板*/
30 public class ForecastDisplay implements Observer, DisplayElement {
31
32 private float temperature;
33 private float pressure;
34 private Subject weatherData;
35
36 public ForecastDisplay(Subject subject) {
37 this.weatherData = subject;
38 weatherData.registerObserver(this);
39 }
40
41 public void removeObserver() {
42 weatherData.removeObserver(this);
43 }
44
45 public void update(float temp, float humidity, float pressure) {
46 this.temperature = temp;
47 this.pressure = pressure;
48 display();
49 }
50
51 public void display() {
52 System.out.println("ForecastDisplay conditions:" + temperature + "F degrees and " + pressure + "Pa");
53 }
54
55 }
56
57 /*气象状况布告板略*/
代码测量试验：
1 public class ObserverTest {
2
3 @Test
4 public void test() {
5 WeatherData weatherDate = new WeatherData();
6 CurrentConditionsDisplay ccDisplay = new CurrentConditionsDisplay(weatherDate);
7 ForecastDisplay fcDisplay = new ForecastDisplay(weatherDate);
8 weatherDate.setMeasurements(12.3f, 38.6f, 130f);
9 ccDisplay.removeObserver();
10 weatherDate.setMeasurements(12.3f, 38.6f, 130f);
11 fcDisplay.removeObserver();
12 weatherDate.setMeasurements(12.3f, 38.6f, 130f);
13 System.out.println("notify ok");
14 }
15 }
运营结果：
1 CurrentConditionsDisplay conditions:12.3F degrees and 38.6% humidity
2 ForecastDisplay conditions:12.3F degrees and 130.0Pa
3 com.project.design.observer.CurrentConditionsDisplay is removed.
4 ForecastDisplay conditions:12.3F degrees and 130.0Pa
5 com.project.design.observer.ForecastDisplay is removed.
6 notify ok
Java
JDK中也设有已经定义好的观看者情势，在java.util包中(Observable(核心),
Observer(观看者))，大家风乐趣能够自个儿领悟下。java中的观看者能够手动从主旨中拉取数据，大旨也得以积极去推送数据。