Exchanger Exchanger 类表示一种两个线程可以进行互相交换对象的会和点。
只能用于两个线程之间，并且两个线程必须都到达汇合点才会进行数据交换。

package com.didispace;

import java.util.concurrent.Exchanger;

/**
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 * [本代码对应视频地址:http://study.163.com/course/introduction/1004176043.htm]
 */
public class ExchangerTest1 {

    public static void main(String[] args) {
        Exchanger<String> exchanger = new Exchanger<String>();
        ExchangerRunnable exchangerRunnable1 = new ExchangerRunnable(exchanger, "A");
        ExchangerRunnable exchangerRunnable2 = new ExchangerRunnable(exchanger, "B");

//              new Thread(exchangerRunnable1).start();
//              new Thread(exchangerRunnable2).start();

        Exchanger<String> exchanger2 = new Exchanger<String>();
        ExchangerRunnable exchangerRunnable3 = new ExchangerRunnable(exchanger2, "C");
        ExchangerRunnable exchangerRunnable4 = new ExchangerRunnable(exchanger2, "D");
        new Thread(exchangerRunnable1).start();
        new Thread(exchangerRunnable2).start();
        new Thread(exchangerRunnable3).start();
        new Thread(exchangerRunnable4).start();
    }
}

class ExchangerRunnable implements Runnable {

    Exchanger<String> exchanger = null;
    String object = null;

    public ExchangerRunnable(Exchanger<String> exchanger, String object) {
        this.exchanger = exchanger;
        this.object = object;
    }

    public void run() {
        try {
            Object previous = this.object;
            System.out.println(Thread.currentThread().getName() + "交换前：" + this.object);
            if ("C".equals(previous)) {
                Thread.sleep(3000);
                System.out.println(Thread.currentThread().getName() + "对数据C的处理耗时3s");
            } else if ("D".equals(previous)) {
                Thread.sleep(4000);
                System.out.println(Thread.currentThread().getName() + "对数据D的处理耗时4s");
            } else if ("A".equals(previous)) {
                Thread.sleep(3000);
                System.out.println(Thread.currentThread().getName() + "对数据A的处理耗时3s");
            } else if ("B".equals(previous)) {
                Thread.sleep(4000);
                System.out.println(Thread.currentThread().getName() + "对数据B的处理耗时4s");
            }
            //两个对象必须在此处汇合,只有一个线程调用change方法是不会进行数据交换的
            this.object = this.exchanger.exchange(this.object);
            System.out.println(Thread.currentThread().getName() + " 交换后: " + this.object);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}