java设计模式-观察者模式

观察者模式定义:

观察者模式定义了一种一对多的依赖关系，让多个观察者对象同时监听某一个主题对象。

这个主题对象在状态上发生变化时，会通知所有观察者对象，让它们能够自动更新自己。

观察者模式的组成:

1.主题

2.观察者

程序代码例子:

package com.ming.mode.observer;


/**
 * 创建主题接口对象 
 * @author mingge
 *
 */
public interface Subject {

    void registerObserver(Observer observer);
    void removeObserver(Observer observer);
    void notifyObservers();
}

package com.ming.mode.observer;

/**
 * 创建观察者接口
 * @author mingge
 *
 */
public interface Observer {

    void update(float t,float b,float ts);
}

package com.ming.mode.observer;

public interface DisplayElement {

    void display();
}

package com.ming.mode.observer;

import java.util.ArrayList;


/**
 * 创建主题接口实现对象
 * @author mingge
 *
 */
public class WeatherData implements Subject{

    private ArrayList<Observer> observers;
    
    private float temperature;
    
    private float humidity;
    
    private float pressure;
    
    public WeatherData() {
        observers=new ArrayList<Observer>();
    }
    
    @Override
    public void registerObserver(Observer observer) {
        observers.add(observer);
        
    }

    @Override
    public void removeObserver(Observer observer) {
        int i=observers.indexOf(observer);
        if(i>=0){
            observers.remove(i);
        }
        
    }

    @Override
    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();
    }
    
    public void setMeasurement(float a,float b,float c){
        this.temperature=a;
        this.humidity=b;
        this.pressure=c;
        measurementsChanged();
    }
    
}

package com.ming.mode.observer;

public class CourrentObserver implements Observer,DisplayElement {
    
    private float temperature;
    
    private float humidity;
    
    private Subject weatherData;
    
    public CourrentObserver(Subject weatherData1) {
        this.weatherData=weatherData1;
        weatherData.registerObserver(this);
    }

    @Override
    public void display() {
        System.out.println("temperature:"+temperature+",humidity:"+humidity);
        
    }

    @Override
    public void update(float t, float b, float ts) {
       this.temperature=t;
       this.humidity=b;
       display();
        
    }

}

package com.ming.mode.observer;

public class Test {

    public static void main(String[] args) {
        WeatherData weatherData=new WeatherData();
        CourrentObserver o=new CourrentObserver(weatherData);
        weatherData.setMeasurement(21, 32, 32);
        weatherData.setMeasurement(20, 31, 32);
    }
}

java内置观察模式的实现

package com.ming.mode.observer.inner;

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 t,float b,float c){
        this.temperature=t;
        this.humidity=b;
        this.pressure=c;
        measurementsChanged();
    }
    
    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;
    }
    
    
    
}

package com.ming.mode.observer.inner;

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

import com.ming.mode.observer.DisplayElement;

public class CurrentConditionsDisplay implements Observer,DisplayElement{
    
    private Observable observable;
    
    private float temperature;
    
    private float humidity;
    
    public CurrentConditionsDisplay(Observable observable){
        this.observable=observable;
        observable.addObserver(this);
    }
    
    
    @Override
    public void display() {
        System.out.println("temperature:"+temperature+",humidity:"+humidity);
        
    }

    @Override
    public void update(Observable o, Object arg) {
        if(o instanceof WeatherData){
            WeatherData w=(WeatherData)o;
            this.temperature=w.getTemperature();
            this.humidity=w.getHumidity();
            display();
        }
    }

    
}

package com.ming.mode.observer.inner;
public class Test {

    public static void main(String[] args) {
        WeatherData weatherData=new WeatherData();
        CurrentConditionsDisplay o=new CurrentConditionsDisplay(weatherData);
        weatherData.setMeasurements(21, 32, 32);
        weatherData.setMeasurements(20, 31, 32);
        System.out.println("ok");
    }
}