Why can't I do something like this?

Question

import java.io.*;
import java.util.*;
class a extends Thread {
    public void run() {
        String s = currentThread().getName();
        System.out.println(s);
public class TestThreadName {
    public static void main (String args[]){
                Thread[] p = new Thread[4];    // declare an array for threads
               for (int i=0; i<4; i++){     
                String pid = Integer.toString(i);   
                a p[i] = new a();
                p.setName(pid);
p[i].start();

Answer 1

I don't know why you invent a class 'a' and when
creating a thread don't use it, since 'a' extends
Thread. I don't know what you wanted to achieve with
your example.
But anyway, Thread cannot be extended. You normally
use the interface runnable and write code into run()
or you create a Thread as an inner class.This is incorrect. There is nothing wrong with extending Thread.