Preventing Thread Execution : 

A thread that's been stopped usually means a thread that's moved to the dead state.

Its your ability to recognize when a thread will get kicked out of running but not be sent back to either runnable or dead.

For the purpose of the understanding, we aren't concerned with a thread blocking on I/O(say, waiting for something to arrive from an input stream from the server).

We are concerned with the following :

1.)  Sleeping.

2.)  Waiting.

3.)  Blocked because it needs an object's lock.