A question about thread

Question

i am learning up on threads.
A Java program can have many threads, and these threads can run concurrently, either asynchronously or synchronously.
so lets say i have 2 classes, A and HelloThread
A
public class A {
     public static void main(String[] args) throws IOException {
        //(lots of codes)
}HelloThread
public class HelloThread extends Thread {
    public void run() {
        System.out.println("Hello from a thread!");
    public static void main(String args[]) {
        (new HelloThread()).start();
}this is what i am confused.
both classes have public static void main(), is that possible?
if no, then what command makes the thread run concurrently?
(since it says many threads can run concurrently)
i m soo confused.
tq

Answer 1

When you run a Java program the java command gives the name of the main class. The interpretter looks in the class you name for a main() method. There's nothing special about the method, appart from it being used this way. It doesn't matter if there are identical methods in other classes because you tell the interpretter which one to look in.
By the way, it's not good practice to subclass Thread this way. To run code in a Thread, create a class (or, very often and anoymous class object) which implements Runnable and use the Runnable object in the constructor of Thread.