sleep和wait方法區別

方法區別

• sleep方法
  sleep讓出cpu資源，但是不會釋放鎖，不干涉鎖行爲；
  哪裏都可以使用
• wait方法
  wait是既讓出cpu資源，又會釋放鎖資源；
  一般使用在同步方法或者同步代碼塊中

案例分析

public class WaitSleepDemo {

    public static void main(String[] args) throws InterruptedException {
        final Object lock = new Object();

        new Thread(() -> {
            System.out.println("Thread A is waiting for the lock");
            synchronized (lock) {
                System.out.println("Thread A get lock");
                try {
                    Thread.sleep(20);
                    System.out.println("Thread A do wait method");
                    lock.wait(1000);
                    System.out.println("Thread A done");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }).start();

        Thread.sleep(10);

        new Thread(() -> {

            System.out.println("Thread B is waiting for the lock");
            synchronized (lock) {
                System.out.println("Thread B get lock");
                try {
                    System.out.println("Thread B is sleeping 10 ms");
                    Thread.sleep(10);
                    System.out.println("Thread B done");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }).start();
    }
}

執行結果：

public class WaitSleepDemo2 {

    public static void main(String[] args) throws InterruptedException {
        final Object lock = new Object();

        new Thread(() -> {
            System.out.println("Thread A is waiting for the lock");
            synchronized (lock) {
                System.out.println("Thread A get lock");
                try {
                    Thread.sleep(20);
                    System.out.println("Thread A do wait method");
                    Thread.sleep(1000);
                    System.out.println("Thread A done");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }).start();

        Thread.sleep(10);

        new Thread(() -> {

            System.out.println("Thread B is waiting for the lock");
            synchronized (lock) {
                System.out.println("Thread B get lock");
                try {
                    System.out.println("Thread B is sleeping 10 ms");
                    lock.wait(10);
                    System.out.println("Thread B done");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }).start();
    }
}

總結

從上面兩個案例打印可以看得出，第一個案例的A線程執行wait方法時，獲取到鎖的；但是第二個案例A線程執行的wait方法處換成sleep之後，B線程無法在A線程結束前獲取到鎖！由此得出文章開始的結論。