synchronization program in java

1class First
2{
3  synchronized public void display(String msg)
4  {
5    System.out.print ("["+msg);
6    try
7    {
8      Thread.sleep(1000);
9    }
10    catch(InterruptedException e)
11    {
12      e.printStackTrace();
13    }
14    System.out.println ("]");
15  }
16}
17
18class Second extends Thread
19{
20  String msg;
21  First fobj;
22  Second (First fp,String str)
23  {
24    fobj = fp;
25    msg = str;
26    start();
27  }
28  public void run()
29  {
30    fobj.display(msg);
31  }
32}
33
34public class MyThread
35{
36  public static void main (String[] args)
37  {
38    First fnew = new First();
39    Second ss = new Second(fnew, "welcome");
40    Second ss1= new Second(fnew,"new");
41    Second ss2 = new Second(fnew, "programmer");
42  }
43}
44