Thread and Runnable

Question

Can anyone please tell me why this code is not executing
FirstClass second=new FirstClass("i m 2nd class");
     second.run();
in the below program.
its show the output like:
i m 3rd class
i m 4rd class
i m in threadi m 3rd class 0
i m 1st class
i m runnablei m 1st class 0
i m in threadi m 4rd class 0
i m runnablei m 1st class 1
i m in threadi m 3rd class 0
i m runnablei m 1st class 2
i m in threadi m 4rd class 0
i m runnablei m 1st class 3
i m in threadi m 3rd class 0
i m runnablei m 1st class 4
i m in threadi m 4rd class 0
i m runnablei m 1st class 5
i m in threadi m 3rd class 0
i m runnablei m 1st class 6
i m in threadi m 4rd class 0
but it didnot tell me about 2nd runnable class why ?
public class MainClass {
public static void main(String[] args) {
     SecondClass third=new SecondClass("i m 3rd class");
     third.start();
     SecondClass fourth=new SecondClass("i m 4rd class");
     fourth.start();
     FirstClass first=new FirstClass("i m 1st class");
     first.run();
     FirstClass second=new FirstClass("i m 2nd class");
     second.run();
class FirstClass implements Runnable{
     private int count;
     private String sq;
     public FirstClass(String str) {
          count=0;
          sq=str;
          System.out.println(str);
public void run() {
     while(true){
     System.out.println("i m runnable" + sq+ " " +count);     
     try {
     count++;
Thread.sleep(500);
     } catch (InterruptedException e) {
class SecondClass extends Thread {
     private int count;
     private String sq;
     public SecondClass(String str) {
          count=0;
          sq=str;
          System.out.println(str);
public void run() {
while(true){
     System.out.println("i m in thread" + sq+ " " +count);
     try {
     Thread.sleep(1000);
     } catch (InterruptedException e) {
}

Answer 1

The reason behind this is that, whenever you implement Runnable in a class and invoke the run() method, no other threads can start after that call. So when you invoke first.run(), the thread "i m 2nd class" doesn't start, i.e,
SecondClass third=new SecondClass("i m 3rd class");
third.start();
SecondClass fourth=new SecondClass("i m 4rd class");
fourth.start();
FirstClass first=new FirstClass("i m 1st class");
first.run();
// this thread won't start and hence the result
FirstClass second=new FirstClass("i m 2nd class");
second.run();
If you had called the run() at the beginning of the program, then neither of the threads would have started
FirstClass first=new FirstClass("i m 1st class");
first.run();
// none of the threads would start
SecondClass third=new SecondClass("i m 3rd class");
third.start();
SecondClass fourth=new SecondClass("i m 4rd class");
fourth.start();
FirstClass second=new FirstClass("i m 2nd class");
second.run();
and that's the reason for your output!