觀察者模式
// 佈告板需要顯示時調用display（）；
public interface DisplayElement {
public void display();
}
//觀察者接口
public interface Observer {
public void update(float temp, float humidity, float pressure);
}
//主題接口
public interface Subject {
public void registerObserver(Observer o);
public void removeObserver(Observer o);
public void notifyObservers();
}
//氣象資料
import java.util.ArrayList;
public class WeatherData implements Subject {
private ArrayList observers;
private float temperature;
private float humidity;
private float pressure;
public WeatherData() {
observers = new ArrayList();
}
//註冊觀察者
public void registerObserver(Observer o) {
observers.add(o);
}
//移除觀察者
public void removeObserver(Observer o) {
int i = observers.indexOf(o);
if (i >= 0) {
observers.remove(i);
}
}
//通知所有觀察者
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();
}
//調用參數設置氣象資料
public void setMeasurements(float temperature, float humidity,
float pressure) {
this.temperature = temperature;
this.humidity = humidity;
this.pressure = pressure;
measurementsChanged();
}
}
//目前狀況佈告板
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);
}
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");
}
}
//氣象站
public class WeatherStation {
public static void main(String[] args) {
WeatherData weatherData = new WeatherData();
CurrentConditionsDisplay currentDisplay = new CurrentConditionsDisplay(
weatherData);
weatherData.setMeasurements(80, 65, 30.4f);
}
}
如果驕傲沒有冷冷拍下，又怎懂得要多努力才走的到遠方，如果夢想不曾墜落懸崖千鈞一髮，又怎曉得執着的人，擁有隱形的翅膀。
--------------------------------------------------《最初的夢想》