Exchanger并发辅助类，允许在并发任务之间交换数据。具体来说Exchanger类在两个线程之间定义同步点。当两个线程到达同步点时，它们交换数据结构。需要注意的是Exchanger类只能同步两个线程。

　　内存一致性效果：对于通过Exchanger成功交换对象的每对线程，每个线程中在exchanger()之前的操作 happen-before从另一线程中相应的exchanger()返回的后续操作。

下面用一对一的生产者-消费者例子进行说明。

　　生产者代码如下：

public class Producer implements Runnable {    private List
     
       buffer;    private Exchanger
      
       
        > exchanger;    public Producer(List
        
          buffer, Exchanger
         
          
           > exchanger) { this.buffer = buffer; this.exchanger = exchanger; } @Override public void run() { int cycle=1; for (int i=0; i<10; i++) { System.out.println("Producer:Cycle "+cycle); for (int j = 1; j <=10; j++) { String msg="Event "+(i*10+j); System.out.println("Producer: "+msg); buffer.add(msg); } try { buffer=exchanger.exchange(buffer);//和消费者交换数据结构 } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("Producer size: "+buffer.size()); cycle++; } }}
          
         
        
       
      
     

　　消费者代码：

public class Consumer implements Runnable {    private List
     
       buffer;    private Exchanger
      
       
        > exchanger;    public Consumer(List
        
          buffer, Exchanger
         
          
           > exchanger) { this.buffer = buffer; this.exchanger = exchanger; } @Override public void run() { int cycle=1; for (int i=0; i<=9; i++) { System.out.println("Consumer: Cycle "+cycle); try { buffer=exchanger.exchange(buffer);//he生产者交换数据结构 } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("Consumer size: "+buffer.size()); for (int j = 1; j <=10; j++) { String msg=buffer.get(0); System.out.println("Consumer: "+msg); buffer.remove(0); } cycle++; } }}
          
         
        
       
      
     

　　运行：

public class Core {    public static void main(String[] args) {        List
     
       buffer1=new ArrayList
      
       ();        List
       
         buffer2=new ArrayList
        
         ();        Exchanger
         
          
           > exchanger=new Exchanger
           
            
             >(); Producer producer=new Producer(buffer1, exchanger); Consumer consumer=new Consumer(buffer2, exchanger); Thread thread1=new Thread(producer); Thread thread2=new Thread(consumer); thread1.start(); thread2.start(); }}