java虚拟机分为隐藏锁,显示锁
其中隐藏说只可以出力公平锁, 显示锁可以出力公平锁和非公平锁

/**
 *显示锁
 * @author Administrator
 */
public class DisplayLock {

    private final Lock lock = new ReentrantLock();

    public void getId() {
        lock.lock();
        System.out.println(UUID.randomUUID());
        lock.unlock();

    }
}


/**
 *隐藏锁(内部锁)
 * @author Administrator
 */
public class SynchronizedLock {

    public synchronized void getId() {
        System.out.println(UUID.randomUUID().toString());
    }

    public void getId2() {
        //this==SynchronizedLock.Class
        synchronized (this) {
            System.out.println(UUID.randomUUID().toString());
        }
    }
    
    //上面两方法相等
}


  SynchronizedLock synchronizedLock = new SynchronizedLock();
        synchronizedLock.getId();
        
        System.out.println("\n");
        DisplayLock displayLock=new DisplayLock();
        displayLock.getId();

显示锁可以细分为很多种,见文档

image.png

关于锁的一些资料
https://www.cnblogs.com/zhengbin/p/5654805.html
https://www.cnblogs.com/hapjin/p/5492880.html
https://www.cnblogs.com/dolphin0520/p/3920373.html