Exchanger（交換者）是一個用於執行緒間協作的工具類。Exchanger用於進行執行緒間的資料交換。它提供一個同步點，在這個同步點兩個執行緒可以交換彼此的資料。這兩個執行緒通過exchange方法交換資料， 如果第一個執行緒先執行exchange方法，它會一直等待第二個執行緒也執行exchange，當兩個執行緒都到達同步點時，這兩個執行緒就可以交換資料，將本執行緒生產出來的資料傳遞給對方。

舉例

class ExchangerTest {

    static class Producer implements Runnable {

        // 生產者、消費者交換的資料結構
 

        private List<String> buffer;

        // 步生產者和消費者的交換物件
        private Exchanger<List<String>> exchanger;

        Producer(List<String> buffer, Exchanger<List<String>> exchanger) {
            this.buffer = buffer;
            this.exchanger = exchanger;
        }

        @Override
        
 
public void run() {
            for (int i = 1; i < 5; i++) {
                for (int j = 1; j <= 3; j++) {
                    System.out.println("生產者裝入" + i + "--" + j);
                    buffer.add("buffer：" + i + "--" + j);
                }

                System.out.println("生產者裝滿，等待與消費者交換...");
                
 
try {
                    exchanger.exchange(buffer);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.err.println("生產者 " + i + ":" + buffer);
            }
        }
    }

    static class Consumer implements Runnable {
        private List<String> buffer;

        private final Exchanger<List<String>> exchanger;

        public Consumer(List<String> buffer, Exchanger<List<String>> exchanger) {
            this.buffer = buffer;
            this.exchanger = exchanger;
        }

        @Override
        public void run() {
            for (int i = 1; i < 5; i++) {
                // 呼叫exchange()與消費者進行資料交換
                try {
                    buffer = exchanger.exchange(buffer);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }

                System.out.println("消費者第" + i + "次提取");
                for (int j = 1; j <= 3; j++) {
                    System.out.println("消費者 : " + buffer.get(0));
                    buffer.remove(0);
                }
            }
        }
    }

    public static void main(String[] args) {
        List<String> buffer1 = new ArrayList<String>();
        List<String> buffer2 = new ArrayList<String>();

        Exchanger<List<String>> exchanger = new Exchanger<List<String>>();

        Thread producerThread = new Thread(new Producer(buffer1, exchanger));
        Thread consumerThread = new Thread(new Consumer(buffer2, exchanger));

        producerThread.start();
        consumerThread.start();
    }
}

併發工具類（四）兩個執行緒進行資料交換的Exchanger

【死磕Java併發】—–J.U.C之併發工具類：Exchanger