假設要統計EXCEL裡的各個Sheet裡的的資料，可以開多個執行緒分別統計各個Sheet,等各個執行緒都統計完成後再進行彙總，這個時候就要實現如題描述的情景。這裡舉例說明，為了簡化，只是模擬。

 我們知道，java裡的join是指等待該執行緒終止，才繼續往下執行。“join”很形象-把執行緒匯聚回主執行緒來，從多執行緒變回單執行緒。接下來看看程式碼如何實現：

/**
 * 多執行緒統計資料，最後彙總
 *
 * @author showshine.wangsh ([email protected])
 * 
 * @since 1.0
 * @version 2018-03-01 12:02
 * 
 */

public class CountBigDataByJoinTest {

	private static int ai1 = 0;
	private static int ai2 = 0;
	private static int n = 2000000000;
	
	public static void main(String[] args) throws InterruptedException {
		long start = System.nanoTime();
		Thread countThread1 = new Thread(new Runnable() {
			@Override
			public void run() {
				for(int i =0; i < n/2; i++) {
					ai1++;
				}
			}
		});
		countThread1.start();
		Thread countThread2 = new Thread(new Runnable() {
			@Override
			public void run() {
				for(int i =0; i < n/2; i++) {
					ai2++;
				}
			}
		});
		countThread2.start();
		countThread1.join();
		countThread2.join();
		System.out.println(ai1+ ai2);
		System.out.println("use " + (System.nanoTime() - start)/(1000 * 1000) + " ms");
	}

}
 

        根據預期，我們能得到正確列印。而jdk併發包裡提供的CountDownLatch、CyclicBarrier工具類同樣能實現該功能。看示例：

CountDownLatch

public class CountBigDataByCountDownLatchTest {

	static CountDownLatch c = new CountDownLatch(2);
	private static int ai1 = 0;
	private static int ai2 = 0;
	private static int n = 2000000000;
	
	public static void main(String[] args) throws InterruptedException {
		long start = System.nanoTime();
		Thread countThread1 = new Thread(new Runnable() {
			@Override
			public void run() {
				for(int i =0; i < n/2; i++) {
					ai1++;
				}
				c.countDown();
			}
		});
		countThread1.start();
		Thread countThread2 = new Thread(new Runnable() {
			@Override
			public void run() {
				for(int i =0; i < n/2; i++) {
					ai2++;
				}
				c.countDown();
			}
		});
		countThread2.start();
		c.await();
		System.out.println(ai1 + ai2);
		System.out.println("use " + (System.nanoTime() - start)/(1000 * 1000) + " ms");
	}

}
 

CyclicBarrier

public class CountBigDataByCyclicBarrierTest {

	static CyclicBarrier cb = new CyclicBarrier(3);
	private static int ai1 = 0;
	private static int ai2 = 0;
	
	public static void main(String[] args) throws InterruptedException, BrokenBarrierException {
		long start = System.nanoTime();
		Thread countThread1 = new Thread(new Runnable() {
			@Override
			public void run() {
				for(int i =0; i < 100000000; i++) {
					ai1++;
				}
				try {
					cb.await();
				} catch (InterruptedException | BrokenBarrierException e) {
					e.printStackTrace();
				}
			}
		});
		countThread1.start();
		Thread countThread2 = new Thread(new Runnable() {
			@Override
			public void run() {
				for(int i =0; i < 100000000; i++) {
					ai2++;
				}
				try {
					cb.await();
				} catch (InterruptedException | BrokenBarrierException e) {
					e.printStackTrace();
				}
			}
		});
		countThread2.start();
		cb.await();
		System.out.println(ai1 + ai2);
		System.out.println("use " + (System.nanoTime() - start)/(1000 * 1000) + " ms");
	}

}