大话设计模式-观察者模式

　　基本简介：观察者<Observer>模式（有时又被称为发布-订阅<Publish/Subscribe>模式、模型-视图<Model/View>模式、源-收听者<Source/Listener>模式或从属者<Dependents>模式）是软件设计模式的一种。在此种模式中，一个目标物件管理所有相依于它的观察者物件，并且在它本身的状态改变时主动发出通知。这通常透过呼叫各观察者所提供的方法来实现。此种模式通常被用来实作事件处理系统。

　　Demo为老板回来了，前台秘书通知办公室里面看NBA、买股票的各个同事。

　　代码：ObserverMain.java-入口类,Subject.java、ScretarySubject.java-发布者类,Observer.java-观察者抽象类,NBAObserver.java、StockObserver.java-具体观察者类。源码

ObserverMain.java-入口类

package publishSubscribe;

/**
 * 观察者模式
 */
public class ObserverMain{
    public static void main(String[] args){
        ScretarySubject scretary = new ScretarySubject();
        scretary.setSubjectState("the boss is come back,work hardly!");
        NBAObserver nbaObserver = new NBAObserver("NBAObserver", scretary);
        StockObserver stockObserver = new StockObserver("StockObserver", scretary);

        scretary.attach(nbaObserver);
        scretary.attach(stockObserver);
        scretary.notifyObservers();
    }

}

Subject.java、ScretarySubject.java-发布者类

package publishSubscribe;

import java.util.ArrayList;
import java.util.List;

/**
 * 发布者
 */
public class Subject {

  private List<Observer> observerList = new ArrayList<Observer>();

  public void attach(Observer ob) {
    this.observerList.add(ob);
  }

  public void detach(Observer ob) {
    this.observerList.remove(ob);
  }
  
  public void notifyObservers(){
    for(Observer o : observerList){
      o.update();
    }
  }
}

package publishSubscribe;

public class ScretarySubject extends Subject {
  private String subjectState;

  public String getSubjectState() {
    return subjectState;
  }

  public void setSubjectState(String subjectState) {
    this.subjectState = subjectState;
  }

}

Observer.java-观察者抽象类

package publishSubscribe;

/**
 * 观察者
 */
public abstract class Observer{
    public abstract void update();
}

NBAObserver.java、StockObserver.java-具体观察者类

package publishSubscribe;

public class NBAObserver extends Observer {
  private String name;
  private ScretarySubject sub;

  public NBAObserver(String name, ScretarySubject sub) {
    this.name = name;
    this.sub = sub;
  }

  public String getName() {
    return name;
  }

  public void setName(String name) {
    this.name = name;
  }
  
  public ScretarySubject getSub() {
    return sub;
  }

  public void setSub(ScretarySubject sub) {
    this.sub = sub;
  }

  @Override
  public void update() {
    System.out.println( this.name + "：" + sub.getSubjectState());
  }

}

package publishSubscribe;

public class StockObserver extends Observer {
  private String name;
  private ScretarySubject sub;

  public StockObserver(String name, ScretarySubject sub) {
    this.name = name;
    this.sub = sub;
  }

  public String getName() {
    return name;
  }

  public void setName(String name) {
    this.name = name;
  }
  
  public ScretarySubject getSub() {
    return sub;
  }

  public void setSub(ScretarySubject sub) {
    this.sub = sub;
  }

  @Override
  public void update() {
      System.out.println( this.name + "：" + sub.getSubjectState());
  }

}