一个关于lock锁的问题

在线程同步中，在一个线程的finally语句块中用lock.unlock()手工释放锁，该锁就一定能释放吗？？还是说仍然可能没有释放，继续占有呢？如果真是一定释放的话，下面这段程序运行结果却不能证明这个说法。
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;public class ThreadTest {        /**
         * @param args
         */
        
        private int j;
        private Lock lock = new ReentrantLock();
        public static void main(String[] args) {
                // TODO Auto-generated method stub
                ThreadTest tt = new ThreadTest();
                for(int i=0;i<2;i++)
                {
                        new Thread(tt.new Adder()).start();
                        new Thread(tt.new Subtractor()).start();
                }
        }        private class Subtractor implements Runnable
        {                @Override
                public void run() {
                        // TODO Auto-generated method stub
                        while(true)
                        {
                                /*synchronized (ThreadTest.this) {                        
                                        System.out.println("j--=" + j--);
                                        //这里抛异常了，锁能释放吗？
                                }*/
                                lock.lock();
                                try
                                {
                                        System.out.println("j--=" + j--);
                                }finally
                                {
                                        lock.unlock();
                                }
                        }
                }
                
        }
        
        private class Adder implements Runnable
        {                @Override
                public void run() {
                        // TODO Auto-generated method stub
                        while(true)
                        {
                                /*synchronized (ThreadTest.this) {
                                System.out.println("j++=" + j++);        
                                }*/
                                lock.lock();
                                try
                                {
                                        System.out.println("j++=" + j++);
                                }finally
                                {
                                        lock.unlock();
                                }                                
                        }                        
                }
                
        }
}