Life Cycle of A Thread

There are several states of thread while a thread is alive.

There are several factor which help to proceed the thread after invoking start() method. Invoking of start() method doesn’t mean that the thread has access to CPU and start executing straight away.

Different states of a thread are :

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.

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.

Different states implementing Multiple-Threads are:

A running thread can enter to any non-runnable state, depending on the circumstances.

A thread cannot enters directly to the running state from non-runnable state, firstly it goes to runnable state.

Some non-runnable states:

Sleeping

On this state, the thread is still alive but it is not runnable, it might be return to runnable state later, if a particular event occurs. On this state a thread sleeps for a specified amount of time. You can use the method sleep( ) to stop the running state of a thread.

static void sleep(long millisecond) throws InterruptedExceptio

Waiting for Notification

A thread waits for notification from another thread. The thread sends back to runnable state after sending notification from another thread.

final void wait(long timeout) throws InterruptedException

final void wait(long timeout, int nanos) throws InterruptedException

final void wait() throws InterruptedException

Blocked on I/O

The thread waits for completion of blocking operation. A thread can enter on this state because of waiting I/O resource. In that case the thread sends back to runnable state after availability of resources.

Blocked for joint completion

The thread can come on this state because of waiting the completion of another thread.

Blocked for lock acquisition

The thread can come on this state because of waiting to acquire the lock of an object.

Methods that can be applied apply on a Thread:

Method	Return Type	Description
currentThread( )	Thread	Returns an object reference to the thread in which it is invoked.
getName( )	String	Retrieve the name of the thread object or instance.
start( )	void	Start the thread by calling its run method.
run( )	void	This method is the entry point to execute thread, like the main method for applications.
sleep( )	void	Suspends a thread for a specified amount of time (in milliseconds).
isAlive( )	boolean	This method is used to determine the thread is running or not.
activeCount( )	int	This method returns the number of active threads in a particular thread group and all its subgroups.
interrupt( )	void	The method interrupt the threads on which it is invoked.
yield( )	void	By invoking this method the current thread pause its execution temporarily and allow other threads to execute.
join( )	void	This method and  join(long millisec) Throws InterruptedException.  These two methods are invoked on a thread. These are not returned until either the thread has completed or it is timed out respectively.