Java Thread Programming 1.8.3 - Inter-thread Communication

答案：
CubbyHole Example
 
The class CubbyHole (see Listing 8.9) simulates a cubbyhole. A cubbyhole is a slot that can have only one item in it at a time. One thread puts an item into the slot and another thread takes it out. If a thread tries to put an item into a cubbyhole that is already occupied, the thread blocks until the slot is available. If a thread tries to remove an item from an empty cubbyhole, the thread blocks until an item is added. In this example, the slot is a reference to an object. This technique allows objects to be handed off from one thread to another in a thread-safe manner.
 
CubbyHole是指一个通道，某一时刻只能容纳一个东西，一个线程放，另一个线程取。如果已经有东西，不能再放，直到东西被取出。如果没有东西，则不能取，直到放进去新东西。下面给出一个线程安全的解决方案：
 
CubbyHole.java
/*
 * Created on 2005-7-14
 *
 * Java Thread Programming - Paul Hyde 
 * Copyright ? 1999 Sams Publishing
 * Jonathan Q. Bo 学习笔记
 * 
 */
package org.tju.msnrl.jonathan.thread.chapter8;
 
/**
 * @author Jonathan Q. Bo from TJU MSNRL
 *
 * Email:jonathan.q.bo@gmail.com
 * Blog:blog.csdn.net/jonathan_q_bo
 *      blog.yesky.net/jonathanundersun
 * 
 * Enjoy Life with Sun!
 * 
 */
public class CubbyHole {
    private Object obj;
 
    public CubbyHole() {
        obj = null;
    }
    
    public synchronized void putIn(Object obj) throws InterruptedException{
        print("putIn() ... begin");
        
        while(this.obj != null){//等待，直到数据被取出
            print("putIn() wait ... begin");
            wait();
            print("putIn() wait ... end");
        }
        
        this.obj = obj;//添加新对象
        notifyAll();//通知其它线程：有对象可取
        
        print("putIn() ... end");
    }
    
    public synchronized Object takeOut()throws InterruptedException{
        print("takeOut() ... begin");
        
        while(obj == null){//等待，直到有数据可以取
            print("takeOut() wait ... begin");
            wait();
            print("takeOut() wait ... end");
        }
        
        Object temp = obj;
        obj = null;//将原数据清空
        notifyAll();//通知其它线程：数据已取出，可填新数据
        
        print("takeOut() ... end");
        
        return temp;
    }
    
    public void print(String msg){
        String temp = Thread.currentThread().getName();
        System.out.println(temp + " - " + msg);
    }
   
}
 
CubbyHoleMain.java
/*
 * Created on 2005-7-14
 *
 * Java Thread Programming - Paul Hyde 
 * Copyright ? 1999 Sams Publishing
 * Jonathan Q. Bo 学习笔记
 * 
 */
package org.tju.msnrl.jonathan.thread.chapter8;
 
/**
 * @author Jonathan Q. Bo from TJU MSNRL
 *
 * Email:jonathan.q.bo@gmail.com
 * Blog:blog.csdn.net/jonathan_q_bo
 *      blog.yesky.net/jonathanundersun
 * 
 * Enjoy Life with Sun!
 * 
 */
public class CubbyHoleMain {
    
    public static void print(String msg){
        String temp = Thread.currentThread().getName();
        System.out.println(temp + " - " + msg);
    }
 
    public static void main(String[] args) {
        final CubbyHole ch = new CubbyHole();
        
        Runnable runA = new Runnable(){
          public void run(){
              try{
                  Thread.sleep(500);//故意晚一些执行，让其它线程先取数据
                  String str;
                  
                  str="multithreads";
                  ch.putIn(str);//可一直存
                  print("run() putIn() " + str);
                  
                  str = "programming";
                  ch.putIn(str);
                  print("run() putIn() " + str);
                  
                  str = "with java";
                  ch.putIn(str);
           

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