Java Lat-15

//Nama Program :lat15.java

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

public class lat15 extends JFrame {
JTextField textNim=new JTextField();
JTextField textNama=new JTextField();
JLabel jLabel1=new JLabel();
JLabel jLabel2=new JLabel();
JLabel jLabel3=new JLabel();
JButton jButton1=new JButton();

public static void main(String args[]){
  lat15 windowku=new lat15();
  windowku.setSize(400,200); 
  Dimension screen =Toolkit.getDefaultToolkit().getScreenSize();
  int lebar=(screen.width-windowku.getSize().width)/2;
  int tinggi=(screen.height-windowku.getSize().height)/2;

  windowku.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  windowku.setLocation(lebar,tinggi);  
  windowku.setVisible(true); 
  windowku.setResizable(false);  
}
public lat15() {
  this.getContentPane().setLayout(null);
  jLabel1.setBounds(new Rectangle(150,0,343,15));
  jLabel1.setText("DATA MAHASISWA"); 
  jLabel2.setBounds(new Rectangle(10,25,86,15));  
  jLabel2.setText("NIM");
  textNim.setBounds(new Rectangle(100,25,187,21));
  textNama.setBounds(new Rectangle(100,60,187,21));
  jLabel3.setBounds(new Rectangle(10,60,86,15));  
  jLabel3.setText("Nama");
  jButton1.setBounds(new Rectangle(150,100,65,20));
  jButton1.setText("OK");

   

  this.setTitle("Arum Ningsih");
  this.getContentPane().add(jLabel1,null);
  this.getContentPane().add(textNim,null);
  this.getContentPane().add(jLabel2,null);
  this.getContentPane().add(textNama,null);
  this.getContentPane().add(jLabel3,null);
 this.getContentPane().add(jButton1,null);
}  

  class changeCase {
  public changeCase() {
}

}
}