Thread: program doesn't woerk

package kmiskaiciuoklis;

import java.awt.BorderLayout;
import javax.swing.JFrame;
//kmiGUI.java turinys
import java.awt.FlowLayout;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JButton;
import javax.swing.JTextField;
import javax.swing.JOptionPane;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import javax.swing.ImageIcon;
import javax.swing.JPanel;


interface Interfeisas {
public JLabel item1 = null;
public JLabel item2 = null;
public JTextField mase = null;
public JTextField ugis = null;
public JButton mygtukas = null;
}

public class Main extends JFrame implements Interfeisas {

private JLabel item1;
private JLabel item2;
private JTextField mase;
private JTextField ugis;
private JButton mygtukas;

public float indeksas;

public Main () {
super("KMI skaiciuokle");

setLayout(new FlowLayout());

item1 = new JLabel("Mase: ");
item1.setToolTipText("Iveskite zmogaus mase kilogramais");
add(item1);

mase = new JTextField(10);
mase.setToolTipText("Iveskite zmogaus mase kilogramais");
add(mase);

item2 = new JLabel("Ugis: ");
item2.setToolTipText("Iveskite zmogaus ugi centimetrais");
add(item2);

ugis = new JTextField(10);
ugis.setToolTipText("Iveskite zmogaus ugi centimetrais");
add(ugis);

mygtukas = new JButton("Skaiciuoti");
add(mygtukas);

HandlerClass handler = new HandlerClass();
mygtukas.addActionListener(handler);

ImageIcon image = new ImageIcon("zmogeliukas.jpg");
//image.setLayout(new BorderLayout());
//JPanel.add(image, BorderLayout.SOUTH);
}

void storulis () {
if (indeksas > 25)
JOptionPane.showMessageDialog (null,"tu storas");
}
void skeletas (){
if (indeksas < 18)
JOptionPane.showMessageDialog(null,"per kudas,eik pavalgyk");
}
void normalus (){
if (indeksas >18 && indeksas <25)
JOptionPane.showMessageDialog(null,"esi normalus");
}


private class HandlerClass implements ActionListener {
public void actionPerformed (ActionEvent event) {
if (event.getSource() == mygtukas) {
try {
float u = Float.parseFloat(ugis.getText()), m = Float.parseFloat(mase.getText());
indeksas = (float)Math.round(m/(u*u/10000)*1000)/1000;
JOptionPane.showMessageDialog(null, "Kuno mases indeksas yra "+indeksas,"Apskaiciuotas KMI",JOptionPane.INFORMATION_MESSAGE);

}
catch (NumberFormatException e) {
System.out.println("error");
}
}


}


}

}

package kmiskaiciuoklis;

import java.util.*;


import javax.swing.JFrame;

public class kmi extends Main{

public static void main (String args[]) {
Thread t1 = new Thread(new thread("pirmas"));
Thread t2 = new Thread(new thread("antras"));
Thread t3 = new Thread(new thread("trecias"));

t1.start();
t2.start();
t3.start();

Main xObj = new Main();
xObj.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE );
xObj.setSize(205,180);
xObj.setVisible(true);
}

}

package kmiskaiciuoklis;
import java.util.*;
/**
*
* @author home
*/
public class thread implements Runnable {
String vardas;
int sk;
Random r = new Random();
public thread(String x){
vardas = x;
sk = r.nextInt(999);
}


public void run(){
try{
System.out.printf("%s kmi yra %d\n", vardas, sk);
Thread.sleep(sk);
System.out.printf("%s suskaiciuota \n", vardas);
}catch(Exception e){}

}}

something is wrong with my program and also I don't know where to use treads and how to do it, actually that should be done by my friend, but it's time to give it for teacher and she still didn't do anything, so i had to do all the work

Please wrap your code in tags.

What is wrong with your code?

You can't initialize inside an interface.

Also, your interface right now appears to not be doing much, if anything, as you have those same variables with types and names exactly the same inside that constructor and that's what you're initializing in that one, not the ones from your interface.