ReentrantLock

ReentrantLock：重入锁的意思。与synchronized作用差不多，区别就是synchronized加锁放锁看不见，而这个重入锁加锁放锁看的见

package thread;

import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class 重入锁 {
    public static void main(String[] args) {
        T t = new T();
        Thread thread1 = new Thread(t);
        Thread thread2 = new Thread(t);
        Thread thread3 = new Thread(t);
        thread1.start();
        thread2.start();
        thread3.start();


    }
}

class T implements Runnable {
    private int count = 10;
    private final ReentrantLock lock = new ReentrantLock();
    @Override
    public void run() {
        while (true) {
            try {
                // 加锁
                lock.lock();
                if (count > 0) {

                    try {
                        Thread.sleep(1000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    System.out.println(--count);
                }
            } finally {
                // 解锁
                lock.unlock();
            }


        }
    }
}

一般把加锁解锁放在try finally语句里面包裹