here is what "Thinking in Java" says about it.
Blocking
A thread can be in any one of four states:
New: The thread object has been created but it hasn�t been started yet so it cannot run.
Runnable: This means that a thread can be run when the time-slicing mechanism has CPU cycles available for the thread. Thus, the thread might or might not be running, but there�s nothing to prevent it from being run if the scheduler can arrange it; it�s not dead or blocked.
Dead: The normal way for a thread to die is by returning from its run( ) method. You can also call stop( ), but this throws an exception that�s a subclass of Error (which means you aren�t forced to put the call in a try block). Remember that throwing an exception should be a special event and not part of normal program execution; thus the use of stop( ) is deprecated in
Java 2. There�s also a destroy( ) method (which has never been implemented) that
you should never call if you can avoid it since it�s drastic and doesn�t release object locks.
Blocked: The thread could be run but there�s something that prevents it. While a thread is in the blocked state the scheduler will simply skip over it and not give it any CPU time. Until a thread reenters the runnable state it won�t perform any operations.
