Can we start a thread twice?

No, A thread can never be started again after starting once. It will throw IllegalThreadStateException.

Example:

ThreadExample.java

/**
 * This program is used to show that we can not start
 * a thread which is already started.
 * @author w3spoint
 */
class Test extends Thread{
	public void run(){
		System.out.println("thread started.");
	}
}
 
public class ThreadExample {
	public static void main(String args[]){
		//creating thread.
		Test thrd = new Test();
 
		//start the thread.
		thrd.start();
 
		//again start the thread which is already started.
		//IllegalThreadStateException here.
		thrd.start();
	}
}

Output:

Exception in thread "main" thread started.
java.lang.IllegalThreadStateException
at java.lang.Thread.start(Unknown Source)
at com.w3spoint.business.ThreadExample.main
(ThreadExample.java:24)

Download this example.

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