线程：Exchanger同步工具

可以在对中对元素进行配对和交换的线程的同步点，类似于交易，A拿着钱到达指定地点，B拿着物品到达指定地点，相互交换，然后各自忙各自的事去了。

 package ch03;

 import java.util.concurrent.Exchanger;

 public class ExchangerTest {

     public static void main(String[] args) {
         final Exchanger<String> changer = new Exchanger<>();
         new Thread(new Runnable() {

             @Override
             public void run() {
                 try{
                     String data1 = "xyy";
                     System.out.println("交换前，"+Thread.currentThread().getName()+"的数据是："+data1);
                     //等待交易
                     String afterChange = changer.exchange(data1);
                     System.out.println("交换后，"+Thread.currentThread().getName()+"的数据是："+afterChange);
                 }catch (Exception e) {
                 }
             }
         }).start();

         new Thread(new Runnable() {

             @Override
             public void run() {
                 try{
                     String data1 = "zy";
                     System.out.println("交换前，"+Thread.currentThread().getName()+"的数据是："+data1);
                     //等待交易
                     String afterChange = changer.exchange(data1);
                     System.out.println("交换后，"+Thread.currentThread().getName()+"的数据是："+afterChange);
                 }catch (Exception e) {
                 }
             }
         }).start();
     }

 }