How is default new thread name given in java?

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