设计模式之观察者模式（二）

package com.dimple.headfirst.observer;

// 1：记得要导入（import）正确的Observer/Observable
import java.util.Observable;

/**
 * 
 * @Title:
 * @Description: 2：我们现在正继承Observable
 * 3：我们不需要追踪观察者了，也不需要管理注册与删除（让超类代劳即可）。
 * 我们把注册、添加、通知的相关代码删除
 */
public class WeatherDataNew extends Observable {
    private float temperature;
    private float humidity;
    private float pressure;

    // 4：我们的构造器不再需要为了记住观察者们而建立数据结构了
    public WeatherDataNew() {

    }

    public void measurementsChanged() {
        // 5: 调用notifyObservers()之前，要先调用setChanged()来指示状态已经改变
        setChanged();
        // 注意：我们没有调用notifyObservers()传送数据对象，这表示我们采用的做法是拉
        notifyObservers();
    }

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

    // 6：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;
    }
}

package com.dimple.headfirst.observer;

import java.util.Observable;
// 1:导入正确的Observer/Observable
import java.util.Observer;

/**
 * 
 * @Title:
 * @Description: 2:我们正在实现java.util.Observer接口
 */
public class CurrentConditionDisplayNew implements Observer, DisplayElement {

    Observable observable;
    private float temperature;
    private float humidity;

    // 3：构造器需要 Observable当参数，并将 CurrentConditionsDisplay对象登记成观察者
    public CurrentConditionDisplayNew(Observable observable) {
        this.observable = observable;
        observable.addObserver(this);
    }

    // 4：改变update方法，增加Observable和数据对象作为参数
    @Override
    public void update(Observable obs, Object arg) {
        // 5：在update()中，先确定可观察者属于WeatherData类型，然后利用getter方法获取温度和湿度测量值，最后调用display() 
        if (obs instanceof WeatherDataNew) {
            WeatherDataNew weatherDataNew = (WeatherDataNew)obs;
            this.temperature = weatherDataNew.getTemperature();
            this.humidity = weatherDataNew.getHumidity();
            display();
        }
    }

    // 显示温度和湿度
    @Override
    public void display() {
        System.out.println("Current conditions: " + temperature + " F degrees and " + humidity + "% humidity");
    }
}

public class WeatherStation {
    public static void main(String[] args) {
        WeatherDataNew weatherDataNew = new WeatherDataNew();
        CurrentConditionDisplayNew currentConditionDisplayNew = new CurrentConditionDisplayNew(weatherDataNew);
        weatherDataNew.setMeasurements(80, 65, 30.4f);
    }
}

// 结果显示
Current conditions: 80.0 F degrees and 65.0% humidity

 protected synchronized void setChanged() {
        changed = true;
    }