的例子小结之.
观察者模式的要点在于,有主题和观察者,主题是"一"方,观察者有很多个,是"多"方,当主题一方有变化时,会通知观察者.
书中的例子是有一个weatherdata对象,有温度,湿度,气压等参数,其中要通知三个不同的观察者,三个观察者要以不同的方式去展示这些数据.
首先是主题接口(subject.java)
package headfirst.observer.weather;
public interface Subject {
public void registerObserver(Observer o);
public void removeObserver(Observer o);
public void notifyObservers();
}
这里实现了注册,移除,和通知各观察者的接口.
观察者接口:
package headfirst.observer.weather;
public interface Observer {
public void update(float temp, float humidity, float pressure);
}
观察者的显示方式接口,因为各观察者会以不同的方式实现该接口
package headfirst.observer.weather;
public interface DisplayElement {
public void display();
}
在weatherdata中,实现subject接口
package headfirst.observer.weather;
import java.util.*;
public class WeatherData implements Subject {
private ArrayList observers;
private float temperature;
private float humidity;
private float pressure;
public WeatherData() {
observers = new ArrayList();
}
public void registerObserver(Observer o) {
observers.add(o);
}
public void removeObserver(Observer o) {
int i = observers.indexOf(o);
if (i >= 0) {
observers.remove(i);
}
}
//通知每个观察者
public void notifyObservers() {
for (int i = 0; i < observers.size(); i++) {
Observer observer = (Observer)observers.get(i);
observer.update(temperature, humidity, pressure);
}
}
public void measurementsChanged() {
notifyObservers();
}
public void setMeasurements(float temperature, float humidity, float pressure) {
this.temperature = temperature;
this.humidity = humidity;
this.pressure = pressure;
measurementsChanged();
}
// other WeatherData methods here
public float getTemperature() {
return temperature;
}
public float getHumidity() {
return humidity;
}
public float getPressure() {
return pressure;
}
}
建立其中一个观察者
package headfirst.observer.weather;
public class CurrentConditionsDisplay implements Observer, DisplayElement {
private float temperature;
private float humidity;
private Subject weatherData;
//注册观察者
public CurrentConditionsDisplay(Subject weatherData) {
this.weatherData = weatherData;
weatherData.registerObserver(this);
}
public void update(float temperature, float humidity, float pressure) {
this.temperature = temperature;
this.humidity = humidity;
display();
}
public void display() {
System.out.println("Current conditions: " + temperature
+ "F degrees and " + humidity + "% humidity");
}
}
客户端:
package headfirst.observer.weather;
import java.util.*;
public class WeatherStation {
public static void main(String[] args) {
WeatherData weatherData = new WeatherData();
CurrentConditionsDisplay currentDisplay =
new CurrentConditionsDisplay(weatherData);
StatisticsDisplay statisticsDisplay = new StatisticsDisplay(weatherData);
ForecastDisplay forecastDisplay = new ForecastDisplay(weatherData);
weatherData.setMeasurements(80, 65, 30.4f);
weatherData.setMeasurements(82, 70, 29.2f);
weatherData.setMeasurements(78, 90, 29.2f);
}
}
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