import java.util.concurrent.locks.ReentrantLock;

public class TestReentrantLock {

  public static void main(String[] args) {

    final ReentrantLock reentrantLock = new ReentrantLock(true);

    reentrantLock.lock();

    new Thread("Thread 1") {

      public void run() {

        for (int i = 1; i < 5; i++) {

          reentrantLock.lock();

          System.out.println(Thread.currentThread().getName() + " print " + i);

          reentrantLock.unlock();

        }

      }

    }.start();

    new Thread("Thread 2") {

      public void run() {

        for (int i = 1; i < 5; i++) {

          reentrantLock.lock();

          System.out.println(Thread.currentThread().getName() + " print " + i);

          reentrantLock.unlock();

        }

      }

    }.start();

    System.out.println(Thread.currentThread().getName() + " Done");

    reentrantLock.unlock();

  }

}

main Done

Thread 1 print 1

Thread 1 print 2

Thread 1 print 3

Thread 1 print 4

Thread 2 print 1

Thread 2 print 2

Thread 2 print 3

Thread 2 print 4