观察者模式:定义了对象之间的一对多依赖,这样依赖,当一个对象改变状态时,它的所有依赖者都会受到通知并自动更新
例子:
package com.zoey.allTest.pattern.headFirst.observerPattern.book;
public interface Subject {
public void registerObserver(Observer o);
public void deleteObserver(Observer o);
public void notifyObservers();//当主题状态改变时,这个方法被调用,通知所有观察者
}
package com.zoey.allTest.pattern.headFirst.observerPattern.book;
public interface Observer {
public void update(float temp, float humidity, float pressure);
}
package com.zoey.allTest.pattern.headFirst.observerPattern.book;
public interface DisplayElement {
public void display();
}
package com.zoey.allTest.pattern.headFirst.observerPattern.book;
public class CurrentConditionsDisplay implements Observer, DisplayElement {
private float temp;
private float humidity;
@SuppressWarnings("unused")
private Subject weatherData;
public CurrentConditionsDisplay(Subject weatherData) {
this.weatherData = weatherData;
weatherData.registerObserver(this);
}
public void update(float temp, float humidity, float pressure) {
this.temp = temp;
this.humidity = humidity;
display();
}
public void display() {
System.out.println(temp + " " + humidity);
}
}
package com.zoey.allTest.pattern.headFirst.observerPattern.book;
import java.util.ArrayList;
public class WeatherData implements Subject {
@SuppressWarnings("rawtypes")
private ArrayList observers;
private float temp;
private float humidity;
private float pressure;
@SuppressWarnings("rawtypes")
public WeatherData() {
observers = new ArrayList();
}
@SuppressWarnings("unchecked")
public void registerObserver(Observer o) {
observers.add(o);
}
public void deleteObserver(Observer o) {
int i = observers.indexOf(o);
if ( i <= 0) {
observers.remove(i);
}
}
public void notifyObservers() {
for (int i = 0; i < observers.size(); i ++) {
Observer o = (Observer) observers.get(i);
o.update(temp, humidity, pressure);
}
}
public void measurementsChanged() {
notifyObservers();
}
public void setMeasurements(float temp, float humidity, float pressure) {
this.temp = temp;
this.humidity = humidity;
this.pressure = pressure;
measurementsChanged();
}
}
package com.zoey.allTest.pattern.headFirst.observerPattern.book;
public class WeatherDataTest {
public static void main(String[] args) {
WeatherData w = new WeatherData();
new CurrentConditionsDisplay(w);
w.setMeasurements(45, 52, 33f);
}
}