设计模式之观察者模式

Wed, 08 Apr 2015 09:36:00 +0000

观察者模式(Observer)

让你的对象知悉现况

使用自定义的Subject(主题)与Observer(观察者模式)

设计原则

找出程序中会变化的方面,然后将其和固定不变的部分分离

在观察者模式中,会改变的事主题的状态,以及观察者的数目和类型.用这个模式,你可以改变依赖于主题状态的对象,却不改变主题.这就叫提前规划

针对接口编程,不针对实现编程

主题与观察者都使用接口:观察者利用主题的接口向主题注册,二主题利用观察者接口通知观察者.这样可以让两者之前运作正常,同时具有松耦合的优点

多用组合,少用继承

观察者模式利用"组合"将许多观察者组合进主题中.对象之前的这种关系不是通过继承产生的,而是在运行时利用组合的方式而产生的.

自己实现观察者模式

我们先定义主题接口

/**
* 主题接口
*/publicinterfaceSubject {
publicvoidregisterObserver(Observer o);
publicvoidremoveObserver(Observer o);
publicvoidnotifyObservers();
}

定义观察者接口

/**
* 观察者接口
*/publicinterfaceObserver {
publicvoidupdate(float temp,float humidity,float pressure);
}

显示元素接口

/**
* 显示元素接口
*/publicinterfaceDisplayElement {
publicvoiddisplay();
}

编写公告板实现,实现了观察者接口与显示元素接口

/**
* 公告板实现
*/publicclassCurrentConditionDisplayimplementsObserver,DisplayElement {
privatefloat temperature;
privatefloat humidity;
private Subject weatherData;
/**
* 构造器需要weatherData对象(也就是主题)作为注册之用
* @param weatherData:天气对象
*/publicCurrentConditionDisplay(Subject weatherData){
this.weatherData=weatherData;
weatherData.registerObserver(this);
}
/**
* display()方法就只是把最近的问的和湿度显示出来
*/@Override
publicvoiddisplay() {
System.out.println("Current conditions:"+temperature+"F degree and "+humidity+"% humidity");
}
/**
* 当update被调用时,我们把温度和湿度保存起来,然后调用display
* @param temp
* @param humidity
* @param pressure
*/@Override
publicvoidupdate(float temp,float humidity,float pressure) {
this.temperature=temp;
this.humidity=humidity;
display();
}
}

天气数据实现主题接口

import java.util.ArrayList;
/**
* 天气数据类实现了Subject(主题)接口
*/publicclassWeatherDataimplementsSubject {
private ArrayList<Observer> observers;
privatefloat temperature;
privatefloat humidity;
privatefloat pressure;
publicWeatherData(){
observers=new ArrayList<>();
}
@Override
publicvoidregisterObserver(Observer o) {
observers.add(o);
}
@Override
publicvoidremoveObserver(Observer o) {
int i=observers.indexOf(o);
if(i>=0){
observers.remove(i);
}
}
@Override
publicvoidnotifyObservers() {
for (Observer observer : observers) {
observer.update(temperature, humidity, pressure);
}
}
/**
* 此方法会在气象值变化时被调用
*/publicvoidmeasurementsChanged(){
notifyObservers();
}
publicvoidsetMeasurements(float temperature,float humidity,float pressure){
this.temperature=temperature;
this.humidity=humidity;
this.pressure=pressure;
measurementsChanged();
}
}

来个测试吧

publicclass WeatherStation {
publicstaticvoidmain(String[] args){
WeatherData weatherData=new WeatherData();
CurrentConditionDisplay currentConditionDisplay=new CurrentConditionDisplay(weatherData);
weatherData.setMeasurements(80,65,30.4f);
}
}
#输出
Current conditions:80.0F degree and 65.0% humidity

使用java自带的Observer

定义显示元素接口

package Observable;
publicinterfaceDisplayElement {
publicvoiddisplay();
}

实现观察者接口和显示元素接口

package Observable;
import java.util.Observable;
import java.util.Observer;
/**
* 天气状况布告板
* Created by jimersylee on
*/publicclassCurrentConditionDisplayimplementsObserver,DisplayElement {
Observable observable;
privatefloat temperature;
privatefloat humidity;
publicCurrentConditionDisplay(Observable observable){
this.observable=observable;
observable.addObserver(this);
}
publicvoidupdate(Observable obs,Object arg){
if(obsinstanceof WeatherData){
WeatherData weatherData=(WeatherData)obs;
this.temperature=weatherData.getTemperature();
this.humidity=weatherData.getHumidity();
display();
}
}
publicvoiddisplay(){
System.out.println("Current conditions:"+temperature+"F degrees and "+humidity+"% humidity");
}
}

实现观察者抽象类

package Observable;
import java.util.Observable;
/**
* 使用java.util内置的观察者模式实现
* Created by jimersylee
*/publicclassWeatherDataextendsObservable {
privatefloat temperature;
privatefloat humidity;
privatefloat pressure;
publicWeatherData(){
}
publicvoidmeasurementsChanged(){
setChanged();
notifyObservers();
}
publicfloatgetTemperature(){
return temperature;
}
publicfloatgetHumidity(){
return humidity;
}
publicfloatgetPressure(){
return pressure;
}
publicvoidsetMeasurements(float temperature,float humidity,float pressure){
this.temperature=temperature;
this.humidity=humidity;
this.pressure=pressure;
measurementsChanged();
}
}

写个测试吧

package Observable;
publicclass WeatherStation {
publicstaticvoidmain(String[] args){
WeatherData weatherData=new WeatherData();
CurrentConditionDisplay currentConditionDisplay=new CurrentConditionDisplay(weatherData);
weatherData.setMeasurements(80,30,33.2f);
}
}
#输出
Current conditions:80.0F degrees and 30.0% humidity

项目地址

java设计模式实现如果觉得有点收获,记得在项目上点star哦!

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