一、sleep()

1、作用
让调用sleep()的线程睡眠（须告知线程要睡多久），线程sleep()就是让出cpu执行权，进入阻塞状态。睡醒以后，线程又会进入就绪状态。

2、释放锁？
sleep()时，线程不释放锁。

二、证明线程sleep()不释放锁？

package about.thread;

public class AboutSleepMethod {

    // 锁对象
    private byte[] lock = new byte[0];

    public void sing() throws InterruptedException {
        // 让run里的线程睡眠，测试线程sleep()会不会释放锁
        synchronized (lock) {
            System.out.println("线程：" + Thread.currentThread().getName() + "准备睡眠！");
            for(int i=0; i<3; i++){
                Thread.sleep(1 * 1000);
                System.out.println(String.valueOf(i));
            }
        }
        System.out.println("线程：" + Thread.currentThread().getName() + "睡眠结束睡眠！");

    }

    public void walk() {
        // 执行run的线程睡眠，测试walk会不会得到执行
        System.out.println("线程：" + Thread.currentThread().getName() + "，准备获取锁执行walk中的synchronized代码块");
        synchronized (lock) {
            System.out.println("线程：" + Thread.currentThread().getName() + "拿到锁，正在执行walk()中的代码块");
        }
    }
}

// 线程A调用sing()方法
class A implements Runnable {

    private AboutSleepMethod aboutSleepMethod;

    public A(AboutSleepMethod aboutSleepMethod) {
        this.aboutSleepMethod = aboutSleepMethod;
    }

    @Override
    public void run() {
        try {
            aboutSleepMethod.sing();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

// 线程B调用walk()方法
// 因为A线程拿到锁lock，并睡眠，
// 而sleep()不会让线程A释放lock锁
// 所以B线程会因为拿不到lock锁而无法执行
// walk()方法中synchronized代码块。
// 通过这个试验就证明了线程sleep()不会释放锁
class B implements Runnable {

    private AboutSleepMethod aboutSleepMethod;

    public B(AboutSleepMethod aboutSleepMethod) {
        this.aboutSleepMethod = aboutSleepMethod;
    }

    @Override
    public void run() {
        aboutSleepMethod.walk();
    }
}

class Run {

    public static void main(String[] args) {
        AboutSleepMethod aboutSleepMethod = new AboutSleepMethod();
        new Thread(new A(aboutSleepMethod), "thread-a").start(); // 启动线程A
        new Thread(new B(aboutSleepMethod),"thread-b").start(); // 启动线程B
    }

}