C线程行为

有人能解释一下为什么这样做有效吗?

    Object ready_lock = new Object();
    Object thread_lock = new Object();
    public static bool able_to_get_lock = false;

    public void GetThreadLock()
    {
        if (Monitor.TryEnter(thread_lock,2))
        {
            able_to_get_lock = true;
        }
    }

    [TestMethod]
    public void ThreadingModelTest()
    {
        Monitor.Enter(ready_lock);
        Thread t1 = new Thread(new ThreadStart(GetThreadLock));
        t1.Start();
        Thread.Sleep(400);
        Assert.IsTrue(able_to_get_lock);

    }

但如果将锁定对象的对象类型更改为字符串(如下所示),则会失败:

    String ready_lock = "Hello";
    String thread_lock = "Hello";

我一时糊涂了。谢谢)