When you are programming with threads, understanding the life cycle of thread is very valuable. While a thread is alive, it is in one of several states. By invoking start() method, it doesn’t mean that the thread has access to CPU and start executing straight away. Several factors determine how it will proceed.

Different states of a thread are :

–>New state, –>Runnable (Ready-to-run) state, –> Running state, –> Dead state, –> Blocked

Defining the different states of the theread is as follows::

1.  New state – After the creations of Thread instance the thread is in this state but before the start() method invocation. At this point, the thread is considered not alive.

2. Runnable (Ready-to-run) state – A thread start its life from Runnable state. A thread first enters runnable state after the invoking of start() method but a thread can return to this state after either running, waiting, sleeping or coming back from blocked state also. On this state a thread is waiting for a turn on the processor.

3. Running state – A thread is in running state that means the thread is currently executing. There are several ways to enter in Runnable state but there is only one way to enter in Running state: the scheduler select a thread from runnable pool.
4. Dead state – A thread can be considered dead when its run() method completes. If any thread comes on this state that means it cannot ever run again.
5. Blocked – A thread can enter in this state because of waiting the resources that are hold by another thread.