import java.util.concurrent.locks.ReentrantLock;

public class ReentrantLockDemo {
    private static ReentrantLock lock = new ReentrantLock();

    public static void main(String[] args) throws InterruptedException {
        new Thread(() -> {
            lock.lock();
            System.out.println(Thread.currentThread().getName());
            try {
                Thread.sleep(3000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            lock.unlock();
        }).start();
        Thread.sleep(10);
        lock.lock();
        System.out.println("main");
        lock.unlock();
    }

}