CountDownLatch

// 減法計數器
public class CountDownLatchDemo {
    public static void main(String[] args) throws InterruptedException {
        // 總數是6 必須要執行任務的時候,再使用!
        CountDownLatch countDownLatch = new CountDownLatch(6);

        for (int i = 0; i < 6; i++) {
            new Thread(() -> {
                System.out.println(Thread.currentThread().getName() + "go out");
                countDownLatch.countDown();
            }, String.valueOf(i)).start();
        }

        countDownLatch.await();//等待計數器歸零,然後再向下執行

        System.out.println("close door");
    }
}
 

CyclicBarrier

// 加法計數器
public class CyclicBarrierDemo {
    public static void main(String[] args) {
        /**
         * 集齊7顆龍珠召喚神龍
         */
        // 召喚龍珠的執行緒
        CyclicBarrier cyclicBarrier = new CyclicBarrier(7, () -> {
            System.out.println("召喚神龍成功~");
        });

        for (int i = 0; i < 7; i++) {
            final int temp = i;
            // lambda能操作到i麼
            new Thread(()->{
                System.out.println(Thread.currentThread().getName() + "收集" + temp + "個龍珠");
                try {
                    cyclicBarrier.await();// 等待
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } catch (BrokenBarrierException e) {
                    e.printStackTrace();
                }
            }).start();
        }
    }
}
 

Semaphore

public class SemaphoreDemo {
    public static void main(String[] args) {
        // 執行緒數量: 停車位! 限流!
        Semaphore semaphore = new Semaphore(3);

        for (int i = 0; i < 6; i++) {
            new Thread(() -> {
                // acquire() 得到
                try {
                    semaphore.acquire();
                    System.out.println(Thread.currentThread().getName() + "搶到車位");
                    TimeUnit.SECONDS.sleep(2);
                    System.out.println(Thread.currentThread().getName() + "離開車位");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } finally {
                    // release() 釋放
                    semaphore.release();
                }

            }, String.valueOf(i)).start();
        }
    }
}