How is default new thread name given in java?

When I run this program

public class Fabric extends Thread {
    public static void main(String[] args) {
        Thread t1 = new Thread(new Fabric());
        Thread t2 = new Thread(new Fabric());
        Thread t3 = new Thread(new Fabric());
        t1.start();
        t2.start();
        t3.start();
    }
    public void run() {
        for(int i = 0; i < 2; i++)
        System.out.print(Thread.currentThread().getName() + " ");
    }
}

I get output

Thread-1 Thread-5 Thread-5 Thread-3 Thread-1 Thread-3

Is there any specific reason why the threads are given names with odd numbers - 1, 3, 5... Or is it unpredictable?

---

new Thread(new Fabric());

Since Fabric is a Thread, you created 2 threads here :)

JDK8 code:

/* For autonumbering anonymous threads. */
private static int threadInitNumber;
private static synchronized int nextThreadNum() {
    return threadInitNumber++;
}

---

The default numeric value in the Thread name is an incremented value unless the name is specified when creating the Thread. Fabric extends Thread , and you are passing the Fabric instance to create another Thread - thus the internal Thread counter is incremented twice as 2 threads are created during the process.

---

If you change the program like given below you will get the thread numbering in sequence.

    public class Fabric extends Thread {
    public static void main(String[] args) {
        Thread t1 = new Fabric();
        Thread t2 = new Fabric();
        Thread t3 = new Fabric();
        t1.start();
        t2.start();
        t3.start();
    }
    public void run() {
        for(int i = 0; i < 2; i++)
            System.out.print(Thread.currentThread().getName() + " ");
    }
}

and the output is

Thread-0 Thread-2 Thread-2 Thread-1 Thread-0 Thread-1

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