观察者模式-jdk

灰太狼 2022-07-12 12:17 119阅读 0赞

package b\_Observer.jdk;

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

interface DisplayElement \{  
void display();  
\}

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

// 将当前对象添加为观察者
    public CurrentConditionsDisplay(Observable observable) {
        this.observable = observable;
        observable.addObserver(this);
    }
    
    public void update(Observable o, Object arg) {
        if (o instanceof WeatherData) {
            WeatherData weatherData = (WeatherData) o;
            this.humidity = weatherData.getHumidity();
            this.pressure = weatherData.getPressure();
            display();
        }
    }
    
    public void display() {
        System.out.println(humidity + " " + pressure);
    }

\}  
package b\_Observer.jdk;

import java.util.Observable;

public class WeatherData extends Observable \{  
private float temperature;  
private float humidity;  
private float pressure;

public WeatherData() {
    }
    
    public void measurementsChanged() {
        //notifyObservers()调用之前要先setChanged()表示数据已经改变
        setChanged();
        //使用此方法没有传送数据对象，表示采用的方式是'拉'
        notifyObservers();
    }
    
    public void setMeasurements(float temperature, float humidity,
            float pressure) {
        this.temperature = temperature;
        this.humidity = humidity;
        this.pressure = pressure;
        measurementsChanged();
    }
    
    //数据采用拉的方式，所以需要提供get()
    public float getTemperature() {
        return temperature;
    }
    
    public float getHumidity() {
        return humidity;
    }
    
    public float getPressure() {
        return pressure;
    }

\}  
package b\_Observer.jdk;  
/\*\*  
\* observerable缺点  
\* 1：是类，无法将关键的地方保护起来，由于setChanged()为protected，所以必须继承采用使用此对象  
\* 违反第二原则，多用组合，少用继承  
\*  
\* PropertyChangeListener:javabean里面的观察者模式  
\*  
\*  
\*/  
public class WeatherStation \{  
public static void main(String\[\] args) \{  
WeatherData weatherData = new WeatherData();

//2个布告板(观察者)
        CurrentConditionsDisplay currentDisplay = new CurrentConditionsDisplay(
                weatherData);
    
        weatherData.setMeasurements(80, 65, 10);
        weatherData.setMeasurements(80, 62, 10);
    
    }