代码：Observable对象

mport java.util.Observable;

/**
 * @author
 * @description 天气数据（可观察者）
 * @date 2018/3/7
 */
public class WeatherData extends Observable {

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

    public void setMesurements(float temperature,float humidity,float pressure){
        this.temperature = temperature;
        this.humidity = humidity;
        this.pressure = pressure;
        measurmentsChanged();
    }
    public float temperature;
    public float humidity;
    public float pressure;

    public float getTemperature() {
        return temperature;
    }

    public void setTemperature(float temperature) {
        this.temperature = temperature;
    }

    public float getHumidity() {
        return humidity;
    }

    public void setHumidity(float humidity) {
        this.humidity = humidity;
    }

    public float getPressure() {
        return pressure;
    }

    public void setPressure(float pressure) {
        this.pressure = pressure;
    }
}

public interface Displayment {
    void display();
}

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

/**
 * @authore
 * @description 观察者
 * @date 2018/3/7
 */
public class ForecastDisplay implements Observer,Displayment {

    private float currentPressure = 29.93f;
    private float lastPressure;
    Observable observable;

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

    @Override
    public void display() {
        System.out.println("Forecast conditions: temperature " + currentPressure );
    }

    @Override
    public void update(Observable o, Object arg) {
        WeatherData weatherData = (WeatherData) o;
        lastPressure = currentPressure;
        currentPressure = weatherData.getPressure();
        display();
    }
}

调用数据：

public class WeatherStation {
    public static void main(String[] args) {
        WeatherData weatherData = new WeatherData();
        ForecastDisplay forecastDisplay = new ForecastDisplay(weatherData);
        weatherData.setMesurements(80,65,30);
    }
}