刚才在看****的问答时，发现这个问题。原问题的作者是在观察jstack的输出时提出的疑问，那么BLOCKED和WAITING有什么区别呢？
答复在JDK源码中可以找到，如下是类的一部分注释。
/**
* Thread state for a thread blocked waiting for a monitor lock.
* A thread in the blocked state is waiting for a monitor lock
* to enter a synchronized block/method or
* reenter a synchronized block/method after calling
* {@link Object#wait() }.
*/
BLOCKED,
/**
* Thread state for a waiting thread.
* A thread is in the waiting state due to calling one of the
* following methods:
* {@link Object#wait() } with no timeout
* {@link #join() } with no timeout
* {@link LockSupport#park() }
*
*
* A thread in the waiting state is waiting for another thread to
* perform a particular action.
*
* For example, a thread that has called ()
* on an object is waiting for another thread to call
* () or () on
* that object. A thread that has called ()
* is waiting for a specified thread to terminate.
*/
WAITING,
从中可以清晰的得到线程处于BLOCKED和WAITING状态的场景。
BLOCKED状态
线程处于BLOCKED状态的场景。
- 当前线程在等待一个monitor lock，比如等待执行synchronized代码块或者使用synchronized标记的方法。
- 在synchronized块中循环调用Object类型的wait方法，如下是样例
synchronized(this)
{
while (flag)
{
();
}
// some other code
}
WAITING状态
线程处于WAITING状态的场景。
- 调用Object对象的wait方法，但没有指定超时值。
- 调用Thread对象的join方法，但没有指定超时值。
- 调用LockSupport对象的park方法。
提到WAITING状态，顺便提一下TIMED_WAITING状态的场景。
TIMED_WAITING状态
线程处于TIMED_WAITING状态的场景。
- 调用方法。
- 调用Object对象的wait方法，指定超时值。
- 调用Thread对象的join方法，指定超时值。
- 调用LockSupport对象的parkNanos方法。
- 调用LockSupport对象的parkUntil方法。