import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

public class Main {

  public static void main(String[] args) {
    System.out.println("read to write test");
    ReadWriteLock lock = new ReentrantReadWriteLock();

    lock.readLock().lock(); // get our own read lock
    lock.writeLock().lock(); // upgrade to write lock
    System.out.println("passed");
  }

}

運行結果如下: