观察者模式

Posted on | In |

观察者模式要达到的目的：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现事件处理系统。

1.类图


2.具体实例

A.txt


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腾辉公司需要个java程序员。海景公司需要个动画设计师。仁海公司需要个电工。

Application


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package Observer;

/**
 * Created by 15581 on 2017/11/8.
 */ // Observer.Application.java
public class Application{
   public static void main(String args[]){
      SeekJobCenter center=new SeekJobCenter();
      UniverStudent zhangLin=new UniverStudent(center,"A.txt");
      HaiGui wangHao=new HaiGui(center,"B.txt");
      center.giveNewMess("腾辉公司需要个java程序员。");
      center.notifyObservers();
      center.giveNewMess("海景公司需要个动画设计师。");
      center.notifyObservers();
      center.giveNewMess("仁海公司需要个电工。");
      center.notifyObservers();
      center.giveNewMess("仁海公司需要个电工。");
      center.notifyObservers();
  }
}

B.txt


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腾辉公司需要个java程序员。

HaiGui


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package Observer;

import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;

/**
 * Created by 15581 on 2017/11/8.
 */
public class HaiGui implements Observer{
   Subject subject;
   File myFile;
   HaiGui(Subject subject,String fileName){
      this.subject=subject;
      subject.addObserver(this);
      myFile=new File(fileName);
   }
   public void hearTelephone(String heardMess){
      try{ boolean boo=heardMess.contains("java程序员")||heardMess.contains("软件");
           if(boo){
             RandomAccessFile out=new RandomAccessFile(myFile,"rw");
             out.seek(out.length());
             byte [] b=heardMess.getBytes();
             out.write(b);
             System.out.print("我是一个海归,");
             System.out.println("我向文件"+myFile.getName()+"写入如下内容:");
             System.out.println(heardMess);
           }
           else{
              System.out.println("我是海归,这次的信息中没有我需要的信息");
           }
      }
      catch(IOException exp){
          System.out.println(exp.toString());
      }
  }
}

Observer


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package Observer;

// Observer.Observer.java
public interface Observer{
   public void hearTelephone(String heardMess);
}

SeekJobCenter


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package Observer;

import java.util.ArrayList;

/**
 * Created by 15581 on 2017/11/8.
 */
public class SeekJobCenter implements Subject{
    String mess;
    boolean changed;
    ArrayList<Observer> personList;
    SeekJobCenter(){
       personList=new ArrayList<Observer>();
       mess="";
       changed=false;
    }
    public void addObserver(Observer o){
       if(!(personList.contains(o)))
         personList.add(o);
    }
    public void deleteObserver(Observer o){
       if(personList.contains(o))
         personList.remove(o);
    }
    public void notifyObservers(){
       if(changed){
          for(int i=0;i<personList.size();i++){
            Observer observer=personList.get(i);
            observer.hearTelephone(mess);
          }
          changed=false;
       }
    }
    public void giveNewMess(String str){
       if(str.equals(mess))
             changed=false;
       else{
             mess=str;
             changed=true;
       }
    }
}

Subject


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package Observer;

/**
 * Created by 15581 on 2017/11/8.
 */ // Observer.Subject.java
public interface Subject{
   public void addObserver(Observer o);
   public void deleteObserver(Observer o);
   public void notifyObservers();
}

UniverStudent


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package Observer;

import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;

/**
 * Created by 15581 on 2017/11/8.
 */
public class UniverStudent implements Observer{
   Subject subject;
   File myFile;
   UniverStudent(Subject subject,String fileName){
      this.subject=subject;
      subject.addObserver(this);     //使当前实例成为subject所引用的具体主题的观察者
      myFile=new File(fileName);
   }
   public void hearTelephone(String heardMess){
      try{ RandomAccessFile out=new RandomAccessFile(myFile,"rw");
           out.seek(out.length());
           byte [] b=heardMess.getBytes();
           out.write(b);                               //更新文件中的内容
           System.out.print("我是一个大学生,");
           System.out.println("我向文件"+myFile.getName()+"写入如下内容:");
           System.out.println(heardMess);
      }
      catch(IOException exp){
          System.out.println(exp.toString());
      }
  }
}