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利用java内置的观察者的话,我们不再需要追踪观察者了,也不需要管理注册与删除(让父类代劳即可)。所以我们把注册,添加,通知的代码都删除。
- package com.godinsec;
- import java.util.Observable;
- public class WeatherData extends Observable{
-
- private float temperature;
- private float humidity;
- private float pressure;
-
- public WeatherData(){} //我们的构造方法不再需要为了记住观察者门而建立数据结构了
-
- public void measurementsChanged(){
- setChanged();
- notifyObservers(); //在调用notifyObservers()之前,要先调用setChanged()来指示状态已经改变
- }
-
- public void setMeasurements(float temperature, float humidity, float pressure){
- this.temperature = temperature;
- this.humidity = humidity;
- this.pressure = pressure;
- measurementsChanged();
- }
-
- //这些并不是新方法,只是因为我们要使用“拉”的做法,所以才提醒你有这些方法。观察者会利用这些方法取得WeatherData对象的状//态。
- public float getTemperature(){
- return temperature;
- }
-
- public float getHumidity(){
- return humidity;
- }
-
- public float getPressure(){
- return pressure;
- }
- }
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观察者的做法:
- package com.godinsec;
- import java.util.Observable;
- import java.util.Observer;
- public class CurrentConditionsDisplay implements Observer,DisplayElement{
-
- Observable observable;
- private float temperature;
- private float humidity;
- private float pressure;
-
- public CurrentConditionsDisplay(Observable observable){
- this.observable = observable;
- observable.addObserver(this);
- }
- @Override
- public void display() {
- // TODO Auto-generated method stub
- System.out.println("Current conditions: " + temperature +
- "F degrees and" + humidity + "% humidity");
- }
- @Override
- public void update(Observable o, Object arg) {
- // TODO Auto-generated method stub
- if(o instanceof WeatherData){
- WeatherData weatherData = (WeatherData)o;
- this.temperature = weatherData.getTemperature();
- this.humidity = weatherData.getHumidity();
- this.pressure = weatherData.getPressure();
- display();
- }
- }
- }
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测试类:
- package com.godinsec;
- 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);
-
- weatherData.setMeasurements(38, 45, 43);
- weatherData.setMeasurements(45.7f, 56.2f, 43);
- weatherData.setMeasurements(38.3f, 45.7f, 43.4f);
- }
- }
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