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概要：
观察者模式原理
观察者模式实例
Java内置观察者
github项目：https://github.com/wangjianxiandev/design -
Internet气象站项目：
- 提供温度、气压和温度的接口
- 测量数据更新时需实时的通知第三方
- 需要设计开放性API，便于其他第三方公司也能接入气象站获取数据
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一个通常的设计方案：
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package guanchazhe;
/**
* Created with IntelliJ IDEA.
* Description:
* User: wjx
* Date: 2019-04-14
* Time: 13:08
*/
public class CurrentConditions {
private float mTempature;
private float mPressure;
private float mHumidity;
public void update(float mTempature, float mPressure, float mHumidity){
this.mTempature = mTempature;
this.mPressure = mPressure;
this.mHumidity = mHumidity;
display();
}
public void display(){
System.out.println("温度"+mTempature);
System.out.println("气压"+mPressure);
System.out.println("湿度"+mHumidity);
}
}
package guanchazhe;
/**
* Created with IntelliJ IDEA.
* Description:
* User: wjx
* Date: 2019-04-14
* Time: 13:14
*/
public class InternetWeather {
public static void main(String[] args) {
CurrentConditions currentConditions = new CurrentConditions();
Weather weather = new Weather(currentConditions);
weather.setData(30,150,40);
}
}
package guanchazhe;
/**
* Created with IntelliJ IDEA.
* Description:
* User: wjx
* Date: 2019-04-14
* Time: 13:06
*/
public class Weather {
private float mTemperate;
private float mPressure;
private float mHumidity;
private CurrentConditions currentConditions;
public Weather(CurrentConditions currentConditions){
this.currentConditions = currentConditions;
}
public void dataChange(){
currentConditions.update(getmTemperate(),getmPressure(),getmHumidity());
}
public float getmTemperate() {
return mTemperate;
}
public float getmPressure() {
return mPressure;
}
public float getmHumidity() {
return mHumidity;
}
public void setData(float mTemperate, float mPressure, float mHumidity){
this.mTemperate = mTemperate;
this.mPressure = mPressure;
this.mHumidity = mHumidity;
dataChange();
}
}
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有些问题
1）其他第三方公司接入气象站获取数据的问题
2）无法在运行时动态的添加第三方 -
观察者模式：
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订牛奶业务：到奶站告诉订牛奶登记注册
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奶站，Subject
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用户，Observer
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Subject: 登记注册、移除和通知
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Observer: 接受输入
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观察者模式的使用：对象之间多对一依赖的一种设计方案，被依赖的对象为Subject, 依赖的对象为Observer, Subject通知Observer变化
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重新设计：
Observer
package guanchazhe.update;
/**
* Created with IntelliJ IDEA.
* Description:
* User: wjx
* Date: 2019-04-14
* Time: 14:04
*/
public interface Observer {
public void update(float mTemperature, float mPressure, float mHumidity);
}
Subject
package guanchazhe.update;
/**
* Created with IntelliJ IDEA.
* Description:
* User: wjx
* Date: 2019-04-14
* Time: 14:07
*/
public interface Subject {
public void registerObserver(Observer observer);//注册观察者
public void removeObserver(Observer observer);//删除观察者
public void notifyObservers();//通知观察者
}
Subject
package guanchazhe.update;
import java.util.ArrayList;
/**
* Created with IntelliJ IDEA.
* Description:
* User: wjx
* Date: 2019-04-14
* Time: 14:12
*/
public class Weather implements Subject {
private float mTemperate;
private float mPressure;
private float mHumidity;
//定义观察者列表
private ArrayList<Observer> mObservers;
public Weather(){
mObservers = new ArrayList<Observer>();
}
public void dataChange(){
//通知是要放到数据改变中
notifyObservers();
}
public float getmTemperate() {
return mTemperate;
}
public float getmPressure() {
return mPressure;
}
public float getmHumidity() {
return mHumidity;
}
public void setData(float mTemperate, float mPressure, float mHumidity){
this.mTemperate = mTemperate;
this.mPressure = mPressure;
this.mHumidity = mHumidity;
dataChange();
}
@Override
public void registerObserver(Observer observer) {
mObservers.add(observer);
}
@Override
public void removeObserver(Observer observer) {
if(mObservers.contains(observer)){
mObservers.remove(observer);
}
}
@Override
public void notifyObservers() {
//通知所有对象有新的信息,获取每一个对象更新
for(int i = 0;i<mObservers.size();i++){
mObservers.get(i).update(getmTemperate(), getmPressure(),getmHumidity());
}
}
}
Observer
package guanchazhe.update;
/**
* Created with IntelliJ IDEA.
* Description:
* User: wjx
* Date: 2019-04-14
* Time: 14:08
*/
public class CurrentConditions implements Observer {
private float mTemperature;
private float mPressure;
private float mHumidity;
@Override
public void update(float mTemperature, float mPressure, float mHumidity) {
this.mTemperature = mTemperature;
this.mPressure = mPressure;
this.mHumidity = mHumidity;
display();
}
public void display(){
System.out.println("温度" + mTemperature);
System.out.println("气压"+ mPressure);
System.out.println("湿度" + mHumidity);
}
}
package guanchazhe.update;
/**
* Created with IntelliJ IDEA.
* Description:
* User: wjx
* Date: 2019-04-14
* Time: 14:11
*/
public class ForcastConditions implements Observer {
private float mTemperature;
private float mPressure;
private float mHumidity;
@Override
public void update(float mTemperature, float mPressure, float mHumidity) {
this.mTemperature = mTemperature;
this.mPressure = mPressure;
this.mHumidity = mHumidity;
display();
}
public void display(){
System.out.println("明温度" + mTemperature+1);
System.out.println("明气压"+ mPressure+1);
System.out.println("明湿度" + mHumidity+1);
}
}
Main
package guanchazhe.update;
/**
* Created with IntelliJ IDEA.
* Description:
* User: wjx
* Date: 2019-04-14
* Time: 14:23
*/
public class InternetWeather {
public static void main(String[] args) {
CurrentConditions currentConditions;
ForcastConditions forcastConditions;
Weather weather;
weather = new Weather();
currentConditions = new CurrentConditions();
forcastConditions = new ForcastConditions();
//注册观察者
weather.registerObserver(currentConditions);
weather.registerObserver(forcastConditions);
weather.setData(30,150,40);
weather.removeObserver(forcastConditions);
weather.setData(30, 120,40);
}
}
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Java内置的观察者 ：
- Observable（类）==Subject（接口）实现注册移除删除观察者
- Observer(接口）使用接口是因为update传递的信息，会因为对象不同采用不同的方式
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内置 观察者的注意点：
- Observable因为不是接口所以不能做到多重继承
- 同时通知的时候需要先进行this.setChanged()设置位true才可以进行通知