JAVA内置的观察者模式样本

DisplayElement.java

public interface DisplayElement {
public void display();

}

CurrentConditionsDisplay.java

import java.util.Observer;
import java.util.Observable;

public class CurrentConditionsDisplay implements Observer, DisplayElement {
    Observable observable;
    private float temperature;
    private float humidity;

    public CurrentConditionsDisplay(Observable observable) {
        this.observable = observable;
        observable.addObserver(this);
    }

    public void update(Observable obs, Object arg) {
        if (obs instanceof WeatherData) {
            WeatherData weatherData = (WeatherData) obs;
            this.temperature = weatherData.getTemperature();
            this.humidity = weatherData.getHumidity();
            display();
        }

    }

    public void display () {
        System.out.println("Current coditions: " + temperature
                + "F degress and " + humidity + "% humidity");
    }

}

WeatherData.java

import java.util.Observable;

public class WeatherData extends Observable {

    private float temperature;
    private float humidity;
    private float pressure;

    public WeatherData() {

    }

    public void measurementsChanged () {
        setChanged();
        notifyObservers();
    }

    public void setMeasurements(float temperature, float humidity, float pressure) {
        this.temperature = temperature;
        this.humidity = humidity;
        this.pressure = pressure;
        measurementsChanged();
    }

    public float getTemperature() {
        return temperature;
    }
    public float getHumidity() {
        return humidity;
    }
    public float getPressure() {
        return pressure;
    }

}

WeatherStation.java

public class WeatherStation {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        WeatherData weatherData = new WeatherData();

        CurrentConditionsDisplay currentDisplay = new CurrentConditionsDisplay(weatherData);
        //StatisticsDisplay statisticsDisplay = new StatisticsDisplay(weatherData);
        //ForecastDisplay forecastDisplay = new ForcecastDisplay(weatherData);

        weatherData.setMeasurements(80, 65, 30.4f);
        weatherData.setMeasurements(82, 70, 29.4f);
        weatherData.setMeasurements(78, 90, 29.4f);

    }

}