swings window header

import java.awt.*;
import javax.swing.*;

class Header{
    public static void main(String []args){
      String st1="123456 service hello";
      String arr[]=st1.split(" ");
      String st2=JOptionPane.showInputDialog(null,"Enter string2: ");
      String st3=st1.replace(arr[1],st2);
      JFrame f=new JFrame(st3);
      f.setLayout(null);
      JLabel l=new JLabel(st3);
      l.setBounds(50,10,300,20);
      f.add(l);
      f.setSize(300,100);
      f.setVisible(true);
    }
}