Java多線程併發經常使用類實例之：exchanger

Exchanger能夠在兩個線程之間交換數據，只能是2個線程，他不支持更多的線程之間互換數據。

當線程A調用Exchange對象的exchange()方法後，他會陷入阻塞狀態，直到線程B也調用了exchange()方法，而後以線程安全的方式交換數據，以後線程A和B繼續運行。

public class ThreadLocalTest {  
  
    public static void main(String[] args) {  
        Exchanger<List<Integer>> exchanger = new Exchanger<>();  
        new Consumer(exchanger).start();  
        new Producer(exchanger).start();  
    }  
  
}  
  
class Producer extends Thread {  
    List<Integer> list = new ArrayList<>();  
    Exchanger<List<Integer>> exchanger = null;  
    public Producer(Exchanger<List<Integer>> exchanger) {  
        super();  
        this.exchanger = exchanger;  
    }  
    @Override  
    public void run() {  
        Random rand = new Random();  
        for(int i=0; i<10; i++) {  
            list.clear();  
            list.add(rand.nextInt(10000));  
            list.add(rand.nextInt(10000));  
            list.add(rand.nextInt(10000));  
            list.add(rand.nextInt(10000));  
            list.add(rand.nextInt(10000));  
            try {  
                list = exchanger.exchange(list);  
            } catch (InterruptedException e) {  
                // TODO Auto-generated catch block  
                e.printStackTrace();  
            }  
        }  
    }  
}  
  
class Consumer extends Thread {  
    List<Integer> list = new ArrayList<>();  
    Exchanger<List<Integer>> exchanger = null;  
    public Consumer(Exchanger<List<Integer>> exchanger) {  
        super();  
        this.exchanger = exchanger;  
    }  
    @Override  
    public void run() {  
        for(int i=0; i<10; i++) {  
            try {  
                list = exchanger.exchange(list);  
            } catch (InterruptedException e) {  
                // TODO Auto-generated catch block  
                e.printStackTrace();  
            }  
            System.out.print(list.get(0)+", ");  
            System.out.print(list.get(1)+", ");  
            System.out.print(list.get(2)+", ");  
            System.out.print(list.get(3)+", ");  
            System.out.println(list.get(4)+", ");  
        }  
    }  
}