观察者模式(Observer Pattern) 详细说明
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观察者模式(Observer Pattern): 定义了对象之间的一对多的依赖, 这样一来, 当一个对象改变状态时, 它的全部依赖者都会收到通知并自己主动更新.
用法:
1. 首先新建主题(subject)接口, 负责注冊(register)\删除(remove)\通知(notify)观察者; 观察者(observer)接口,
负责更新(update)数据;
主题(subject)接口: 注冊观察者(registerObserver), 删除观察者(removeObserver), 通知观察者(notifyObservers, 通知全部观察者);
观察者(observer)接口: 更新(update);
代码:
/**
* @time 2014年5月22日
*/
package observer;
/**
* @author C.L.Wang
*
*/
public interface Subject {
public void registerObserver(Observer o);
public void removeObserver(Observer o);
public void notifyObervers();
}
/**
* @time 2014年5月22日
*/
package observer;
/**
* @author C.L.Wang
*
*/
public interface Observer {
public void update(float temp, float humidity, float pressure);
}
/**
* @time 2014年5月22日
*/
package observer;
/**
* @author C.L.Wang
*
*/
public interface DisplayElement {
public void display();
}
2. 实现主题(subject)接口, 通过列表(list)的形式注冊(register)和删除(remove)观察者,
通知(notify)观察者时, 循环调用全部已注冊的观察者的更新(update)动作;
通过接口函数(set), 封装通知(notify)动作, 传入參数并进行通知.
代码:
/**
* @time 2014年5月22日
*/
package observer;
import java.util.ArrayList;
/**
* @author C.L.Wang
*
*/
public class WeatherData implements Subject {
public ArrayList
private float temperature;
private float humidity; //湿度
private float pressure;
public WeatherData() {
observers = new ArrayList
}
/* (non-Javadoc)
* @see observer.Subject#registerObserver(observer.Observer)
*/
@Override
public void registerObserver(Observer o) {
// TODO Auto-generated method stub
observers.add(o);
}
/* (non-Javadoc)
* @see observer.Subject#removeObserver(observer.Observer)
*/
@Override
public void removeObserver(Observer o) {
// TODO Auto-generated method stub
int i = observers.indexOf(o);
if (i>=0) {
observers.remove(i);
}
}
/* (non-Javadoc)
* @see observer.Subject#notifyObervers()
*/
@Override
public void notifyObervers() {
// TODO Auto-generated method stub
for (int i=0; i Observer observer = (Observer)observers.get(i); observer.update(temperature, humidity, pressure); } } public void measurementsChanged() { notifyObervers(); } public void setMeasurements(float temperature, float humidity, float pressure) { this.temperature = temperature; this.humidity = humidity; this.pressure = pressure; measurementsChanged(); } } 3. 实现观察者(observer)接口, 主要保存收到的数据, 并实现更新(update)动作, 即把数据保存在本地; 在构造函数中, 把自己注冊(register)入, 传入的主题(subject)參数, 使主题能够通知观察者. 代码: /** * @time 2014年5月22日 */ package observer; /** * @author C.L.Wang * */ public class CurrentConditionsDisplay implements Observer, DisplayElement { private float temperature; private float humidity; private Subject weatherData; public CurrentConditionsDisplay(Subject weatherData) { this.weatherData = weatherData; weatherData.registerObserver(this); } /* (non-Javadoc) * @see observer.DisplayElement#display() */ @Override public void display() { // TODO Auto-generated method stub System.out.println("Current conditions: " + temperature + "F degrees and " + humidity + "% humidity"); } /* (non-Javadoc) * @see observer.Observer#update(float, float, float) */ @Override public void update(float temperature, float humidity, float pressure) { // TODO Auto-generated method stub this.temperature = temperature; this.humidity = humidity; display(); } } package observer; import java.util.*; public class ForecastDisplay implements Observer, DisplayElement { private float currentPressure = 29.92f; private float lastPressure; private WeatherData weatherData; public ForecastDisplay(WeatherData weatherData) { this.weatherData = weatherData; weatherData.registerObserver(this); } public void update(float temp, float humidity, float pressure) { lastPressure = currentPressure; currentPressure = pressure; display(); } public void display() { System.out.print("Forecast: "); if (currentPressure > lastPressure) { System.out.println("Improving weather on the way!"); } else if (currentPressure == lastPressure) { System.out.println("More of the same"); } else if (currentPressure < lastPressure) { System.out.println("Watch out for cooler, rainy weather"); } } } package observer; import java.util.*; public class StatisticsDisplay implements Observer, DisplayElement { private float maxTemp = 0.0f; private float minTemp = 200; private float tempSum= 0.0f; private int numReadings; private WeatherData weatherData; public StatisticsDisplay(WeatherData weatherData) { this.weatherData = weatherData; weatherData.registerObserver(this); } public void update(float temp, float humidity, float pressure) { tempSum += temp; numReadings++; if (temp > maxTemp) { maxTemp = temp; } if (temp < minTemp) { minTemp = temp; } display(); } public void display() { System.out.println("Avg/Max/Min temperature = " + (tempSum / numReadings) + "/" + maxTemp + "/" + minTemp); } } 4. 測试, 创建不同的观察者(observer), 并把主题(subject)作为參数传入, 通知观察者. 代码: /** * @time 2014年5月22日 */ package observer; /** * @author C.L.Wang * */ public class WeatherStation { /** * @param args */ public static void main(String[] args) { // TODO Auto-generated method stub WeatherData weatherData = new WeatherData(); CurrentConditionsDisplay currentConditionsDisplay = new CurrentConditionsDisplay(weatherData); //new的时候进行注冊 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); } } 5. 输出: Current conditions: 80.0F degrees and 65.0% humidity Avg/Max/Min temperature = 80.0/80.0/80.0 Forecast: Improving weather on the way! Current conditions: 82.0F degrees and 70.0% humidity Avg/Max/Min temperature = 81.0/82.0/80.0 Forecast: Watch out for cooler, rainy weather Current conditions: 78.0F degrees and 90.0% humidity Avg/Max/Min temperature = 80.0/82.0/78.0 Forecast: More of the same 面向对象的原则: 为了设计对象和工作之间松散耦合的交互. 相关文章
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