Why can't we call the start method twice on a same instance of the Thread object?

Question

I was reading about threads and found that we can\'t call the start method twice on the same thread instance. But I didn\'t understand the exact reason for the same. So why

Answer 1

This is my opinion, It is due to Thread id. Thread scheduler is identifying the thread through the thread id. It is unique real number. Please find below code,

    public class StartTwice extends Thread {

    public void run() {
        System.out.println("running...");
    }

    public static void main(String[] args) {

        StartTwice start1 = new StartTwice();
        System.out.println("Thread id: " + start1.getId());
        start1.start();

        start1 = new StartTwice();
        System.out.println("Thread id: " + start1.getId());
        start1.start();
    }

}

Output is:

Thread id: 10
Thread id: 11
running...
running...

When I re-instantiate the start1 object. A new thread id is created.

PS: Even a thread is done, we can't use the same object (thread id) second time. Until or unless the JVM is reuse that id.