How to check if a thread is already started or not in Java?

Question

I am having a class which extends Thread.

I will start the thread at some point.

After some time I need to check if that thread is already started or not?

So that I can start the thread at that particular point.

My thread class will be,

public class BasicChatListener extends Thread{

    public void run(){


    }

}

I need the know the particular thread of a BasicChatListener class is running or not ? Because I have multiple threads are already running in my application.

How our stack members will help me.

You held the reference to the specified `BasicChatListener`, don't you? — johnchen902, Jul 02 '13 at 09:50
Looks like you need to create a start just one listener. Can you create instance of the `BasicChatListener` and start it at the same time? — denis.solonenko, Jul 02 '13 at 09:50
@Vignesh Vino But How to refer the `BasicChatListener` thread particularly for checking ? Even I can have multiple threads in my application ? That is what I have asked. — Human Being, Jul 02 '13 at 10:37
I need the know the particular thread of a class is running or not ? — Human Being, Jul 02 '13 at 10:41

Brian Agnew · Answer 1 · 2013-07-02T10:18:27.730

6

You can use Thread.getState() and use the corresponding states.

Note that by the time you read this state it may have changed, but you may be able to determine something of interest. Check out this state diagram for the available transitions.

edited Jul 02 '13 at 10:18

answered Jul 02 '13 at 09:47

Brian Agnew

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How to refer the `BasicChatListener` thread particularly for check ? – Human Being Jul 02 '13 at 10:38
It is probably better to use a Monitor, Semaphore, or some other shared object as the Thread states are a tad limited. Running may not mean started to the degree you want. – Andrew Scott Evans Jun 28 '17 at 17:41
Link not working!!!!!!!!!!! – Rahul Rastogi Feb 19 '18 at 06:32

Ravi K Thapliyal · Answer 2 · 2013-07-02T10:00:38.233

Use either Thread#isAlive()

if (Thread.currentThread().isAlive())

JavaDoc says:

Tests if this thread is alive. A thread is alive if it has been started and has not yet died.

Or, use Thread#getState() as

Thread.State currState = Thread.currentThread().getState();
if (currState != Thread.State.NEW && currState != Thread.State.TERMINATED)

JavaDoc says:

Returns the state of this thread. This method is designed for use in monitoring of the system state, not for synchronization control.

score 1 · Answer 3 · answered Jul 02 '13 at 09:47

1

You can check it with isAlive..

isAlive tests if this thread is alive. A thread is alive if it has been started and has not yet died.

answered Jul 02 '13 at 09:47

Anirudha

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+1 To me, using isAlive is clearer than calling getState and having to check that the state is not new. – matt freake Jul 02 '13 at 09:54

score 1 · Answer 4 · answered Jul 02 '13 at 09:48

1

I use this code Thread.isAlive()

answered Jul 02 '13 at 09:48

nano_nano

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score 1 · Answer 5 · answered Jul 02 '13 at 09:48

You can use GetState()

Returns the state of this thread. This method is designed for use in monitoring of the system state, not for synchronization control.

or boolean isAlive()

Tests if this thread is alive. A thread is alive if it has been started and has not yet died.

score 1 · Answer 6 · answered Jul 02 '13 at 09:48

Thread.isAlive() can determine if a thread is running.

Tests if this thread is alive. A thread is alive if it has been started and has not yet died.

Thread#getState(); can return the exact state of a thread.

Returns the state of this thread. This method is designed for use in monitoring of the system state, not for synchronization control.

How to check if a thread is already started or not in Java?

6 Answers6

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