By puting the "if -statement" inside the run() method, threads get created in order. If a change the "if-statement" to a "while" (same boolean condition), the Threads get created randomly, but it doesn't pass the testing. I'm confused. What is the difference? Thanks!
public class Solution {
    static int count = 15;
    static volatile int createdThreadCount;

    public static void main(String[] args) {
            System.out.println(new GenerateThread());
    }

    public static class GenerateThread extends Thread {

        public GenerateThread(){
            super(String.valueOf(++createdThreadCount));
            start();
        }

        @Override
        public void run() {
            if(createdThreadCount < count){
                GenerateThread thread = new GenerateThread();
                System.out.println(thread);
            }
        }

        @Override
        public String toString() {
            return getName() + " " + "created";
        }
    }
}