A thread can be only in one of five states.
* New: This is the state the thread is in after the Thread instance has been created, but the start() method has not been invoked on the thread. It is a live Thread object, but not yet a thread of execution. At this point, the thread is considered not alive.
* Runnable: This is the state a thread is in when it's eligible to run, but the scheduler has not selected it to be the running thread. A thread first enters the runnable state when the start() method is invoked, but a thread can also return to the runnable state after either running or coming back from a blocked, waiting, or sleeping state. When the thread is in the runnable state, it is considered alive.
* Running: This is the state a thread is in when the thread scheduler selects it (from the runnable pool) to be the currently executing process. A thread can transition out of a running state for several reasons, including because "the thread scheduler felt like it."
* Waiting/blocked/sleeping: This is the state a thread is in when it's not eligible to run.
* Dead: A thread is considered dead when its run() method completes. It may still be a viable Thread object, but it is no longer a separate thread of execution.