حساب الوقت في الجافا

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

public class HowLong {

static long timeStart, timeEnd;

public static void main(String[] args) {
JFrame frm = new JFrame();
JButton btnStart = new JButton("Start");

btnStart.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent ae) {
timeStart = System.currentTimeMillis();
}
});
JButton btnEnd = new JButton("End");
btnEnd.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent ae) {
timeEnd = System.currentTimeMillis();
long time = timeEnd - timeStart;
System.out.println((time / 1000) + " seconds has passed");
}
});
frm.add(btnStart, BorderLayout.NORTH);
frm.add(btnEnd, BorderLayout.SOUTH);
frm.setSize(200, 150);
frm.setVisible(true);
}
}

import java.awt.*;

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

public class HowLong implements ActionListener{

long timeStart, timeEnd;
JFrame frm = new JFrame();
Timer timer = new Timer(2000, this);
JButton btnStart = new JButton("Start");
JButton btnEnd = new JButton("End");

public HowLong() {

btnStart.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent ae) {
timeStart = System.currentTimeMillis();
timer.start();
}
});
btnEnd.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent ae) {
timeEnd = System.currentTimeMillis();
long time = timeEnd - timeStart;
System.out.println((time / 1000) + " seconds has passed");
}
});
frm.add(btnStart, BorderLayout.NORTH);
frm.add(btnEnd, BorderLayout.SOUTH);
frm.setSize(200, 150);
frm.setVisible(true);
}

public void actionPerformed(ActionEvent ae) {
System.out.println("Tow second has passed, the button will be disabled");
btnStart.setEnabled(false);
timer.stop();
}

public static void main(String[] args) {
new HowLong();
}
}

import java.awt.*;