The document contains a Java implementation of a simple stopwatch GUI using Swing. It includes features for starting, stopping, and resetting the timer, with time updates reflected on a JLabel. The stopwatch is created within a custom JPanel, and a JFrame is used to display it.

1. import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class StopWatch extends JPanel
{
private Timer myTimer1;
public static final int ONE_SEC = 1000; //time step in milliseconds
public static final int TENTH_SEC = 100;
private Font myClockFont;
private JButton startBtn, stopBtn, resetBtn;
private JLabel timeLbl;
private JPanel topPanel, bottomPanel;
private int clockTick; //number of clock ticks; tick can be 1.0 s or 0.1 s
private double clockTime; //time in seconds
private String clockTimeString;
public StopWatch()
{
clockTick = 0; //initial clock setting in clock ticks
clockTime = ((double)clockTick)/10.0;
clockTimeString = new Double(clockTime).toString();
myClockFont = new Font("Serif", Font.PLAIN, 50);
timeLbl = new JLabel();
timeLbl.setFont(myClockFont);
timeLbl.setText(clockTimeString);
startBtn = new JButton("Start");
stopBtn = new JButton("Stop");
resetBtn = new JButton("Reset");
myTimer1 = new Timer(TENTH_SEC, new ActionListener() {
public void actionPerformed(ActionEvent evt) {
clockTick++;
clockTime = ((double)clockTick)/10.0;
clockTimeString = new Double(clockTime).toString();
timeLbl.setText(clockTimeString);

2. //System.out.println(clockTime);
}
});
startBtn.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent evt){
myTimer1.start();
}
});
stopBtn.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent evt){
myTimer1.stop();
}
});
resetBtn.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent evt){
clockTick = 0;
clockTime = ((double)clockTick)/10.0;
clockTimeString = new Double(clockTime).toString();
timeLbl.setText(clockTimeString);
}
});
}//end of StopWatch constructor
public void launchStopWatch()
{
topPanel = new JPanel();
topPanel.setBackground(Color.orange);
bottomPanel = new JPanel();
bottomPanel.setBackground(Color.yellow);
topPanel.add(timeLbl);
bottomPanel.add(startBtn);
bottomPanel.add(stopBtn);
bottomPanel.add(resetBtn);
this.setLayout(new BorderLayout());
add(topPanel, BorderLayout.CENTER);
add(bottomPanel, BorderLayout.SOUTH);

3. setSize(300,200);
setBackground(Color.orange);
}//end of launchClock
public static void main(String[] args)
{
MyTestFrame myTestFrame1 = new MyTestFrame();
}
}
class MyTestFrame extends JFrame
{
StopWatch StopWatch1;
public MyTestFrame()
{
super("My Stop Watch");
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
Container myPane = getContentPane();
StopWatch1 = new StopWatch();
StopWatch1.launchStopWatch();
myPane.add(StopWatch1);
pack();
setVisible(true);
}
}
Solution
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class StopWatch extends JPanel
{
private Timer myTimer1;
public static final int ONE_SEC = 1000; //time step in milliseconds
public static final int TENTH_SEC = 100;
private Font myClockFont;

4. private JButton startBtn, stopBtn, resetBtn;
private JLabel timeLbl;
private JPanel topPanel, bottomPanel;
private int clockTick; //number of clock ticks; tick can be 1.0 s or 0.1 s
private double clockTime; //time in seconds
private String clockTimeString;
public StopWatch()
{
clockTick = 0; //initial clock setting in clock ticks
clockTime = ((double)clockTick)/10.0;
clockTimeString = new Double(clockTime).toString();
myClockFont = new Font("Serif", Font.PLAIN, 50);
timeLbl = new JLabel();
timeLbl.setFont(myClockFont);
timeLbl.setText(clockTimeString);
startBtn = new JButton("Start");
stopBtn = new JButton("Stop");
resetBtn = new JButton("Reset");
myTimer1 = new Timer(TENTH_SEC, new ActionListener() {
public void actionPerformed(ActionEvent evt) {
clockTick++;
clockTime = ((double)clockTick)/10.0;
clockTimeString = new Double(clockTime).toString();
timeLbl.setText(clockTimeString);
//System.out.println(clockTime);
}
});
startBtn.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent evt){
myTimer1.start();
}
});
stopBtn.addActionListener(new ActionListener(){

5. public void actionPerformed(ActionEvent evt){
myTimer1.stop();
}
});
resetBtn.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent evt){
clockTick = 0;
clockTime = ((double)clockTick)/10.0;
clockTimeString = new Double(clockTime).toString();
timeLbl.setText(clockTimeString);
}
});
}//end of StopWatch constructor
public void launchStopWatch()
{
topPanel = new JPanel();
topPanel.setBackground(Color.orange);
bottomPanel = new JPanel();
bottomPanel.setBackground(Color.yellow);
topPanel.add(timeLbl);
bottomPanel.add(startBtn);
bottomPanel.add(stopBtn);
bottomPanel.add(resetBtn);
this.setLayout(new BorderLayout());
add(topPanel, BorderLayout.CENTER);
add(bottomPanel, BorderLayout.SOUTH);
setSize(300,200);
setBackground(Color.orange);
}//end of launchClock
public static void main(String[] args)
{
MyTestFrame myTestFrame1 = new MyTestFrame();
}
}
class MyTestFrame extends JFrame

6. {
StopWatch StopWatch1;
public MyTestFrame()
{
super("My Stop Watch");
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
Container myPane = getContentPane();
StopWatch1 = new StopWatch();
StopWatch1.launchStopWatch();
myPane.add(StopWatch1);
pack();
setVisible(true);
}
}