常用的辅助类

CountDownLatch

// 减法计数器
public class CountDownLatchDemo {
    public static void main(String[] args) throws InterruptedException {
        // 总数是6 必须要执行任务的时候,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();//等待计数器归零,然后再向下执行

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

CyclicBarrier

// 加法计数器
public class CyclicBarrierDemo {
    public static void main(String[] args) {
        /**
         * 集齐7颗龙珠召唤神龙
         */
        // 召唤龙珠的线程
        CyclicBarrier cyclicBarrier = new CyclicBarrier(7, () -> {
            System.out.println("召唤神龙成功~");
        });

        for (int i = 0; i < 7; i++) {
            final int temp = i;
            // lambda能操作到i么
            new Thread(()->{
                System.out.println(Thread.currentThread().getName() + "收集" + temp + "个龙珠");
                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) {
        // 线程数量: 停车位! 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() + "抢到车位");
                    TimeUnit.SECONDS.sleep(2);
                    System.out.println(Thread.currentThread().getName() + "离开车位");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } finally {
                    // release() 释放
                    semaphore.release();
                }

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