Timer in Java with GUI

Question

I have created a timer with GUI in Java.

Here's the code:

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.Toolkit;
import java.awt.event.ActionListener;
import java.text.NumberFormat;
import javax.swing.text.NumberFormatter;
import static javax.swing.WindowConstants.EXIT_ON_CLOSE;
public class Counter {
 private JButton button;
 private JFormattedTextField hours;
 private JFormattedTextField minutes;
 private JFormattedTextField seconds;
 private Timer timer;
 private int delay = 1000;
 private ActionListener taskPerformer = new ActionListener() {
 public void actionPerformed(ActionEvent evt) {
 if(sec >= 1) {
 sec = sec - 1;
 seconds.setText(String.valueOf(sec));
 }
 else if(sec == 0 && min > 0) {
 sec = 59;
 min = min - 1;
 seconds.setText(String.valueOf(sec));
 minutes.setText(String.valueOf(min));
 }
 else if(min == 0 && hrs > 0) {
 sec = 59;
 min = 59;
 hrs = hrs - 1;
 seconds.setText(String.valueOf(sec));
 minutes.setText(String.valueOf(min));
 hours.setText(String.valueOf(hrs));
 }
 if(hrs == 0 && min == 0 && sec == 0) {
 Toolkit.getDefaultToolkit().beep();
 JOptionPane.showMessageDialog(null,"Countdown ended!","Ende", JOptionPane.CANCEL_OPTION);
 timer.stop();
 }
 }
 };
 private int hrs;
 private int min;
 private int sec;
 public static void main(String[] args) throws InterruptedException {
 SwingUtilities.invokeLater(Counter::new);
 }
 Counter() {
 JFrame frame = new JFrame();
 frame.setSize(300, 200);
 frame.setDefaultCloseOperation(EXIT_ON_CLOSE);
 JPanel panel = new JPanel(new BorderLayout());
 JPanel subpanel1 = new JPanel(new GridLayout(2, 3));
 /* 
 * The following lines ensure that the user can 
 * only enter numbers.
 */
 NumberFormat format = NumberFormat.getInstance();
 NumberFormatter formatter = new NumberFormatter(format);
 formatter.setValueClass(Integer.class);
 formatter.setMinimum(0);
 formatter.setMaximum(Integer.MAX_VALUE);
 formatter.setAllowsInvalid(false);
 formatter.setCommitsOnValidEdit(true);
 //"labeling"
 JTextField text1 = new JTextField();
 text1.setText("hours:");
 text1.setEditable(false);
 JTextField text2 = new JTextField();
 text2.setText("minutes:");
 text2.setEditable(false);
 JTextField text3 = new JTextField();
 text3.setText("seconds:");
 text3.setEditable(false);
 //fields for minutes and seconds
 hours = new JFormattedTextField(formatter);
 minutes = new JFormattedTextField(formatter);
 seconds = new JFormattedTextField(formatter);
 hours.setText("0");
 minutes.setText("0");
 seconds.setText("0");
 JPanel subpanel2 = new JPanel();
 /*
 * When the user presses the OK-button, the program will
 * start to count down.
 */
 button = new JButton("OK");
 button.addActionListener(new ActionListener() {
 @Override
 public void actionPerformed(ActionEvent actionEvent) {
 hrs = Integer.valueOf(hours.getText());
 min = Integer.valueOf(minutes.getText());
 sec = Integer.valueOf(seconds.getText());
 button.setEnabled(false);
 //Timer for one second delay
 Timer timer = new Timer(delay, taskPerformer);
 timer.start(); 
 }
 });
 //Reset-button
 JButton button2 = new JButton("Reset");
 button2.addActionListener(new ActionListener() {
 @Override
 public void actionPerformed(ActionEvent actionEvent) {
 hours.setText("0");
 minutes.setText("0");
 seconds.setText("0");
 button.setEnabled(true);
 hrs = 0;
 min = 0;
 sec = 0;
 }
 });
 subpanel1.add(text1);
 subpanel1.add(text2);
 subpanel1.add(text3);
 subpanel1.add(hours);
 subpanel1.add(minutes);
 subpanel1.add(seconds);
 subpanel2.add(button);
 subpanel2.add(button2);
 panel.add(subpanel1, BorderLayout.CENTER);
 panel.add(subpanel2, BorderLayout.PAGE_END);
 frame.add(panel);
 frame.setVisible(true);
 }
}

I would appreciate any suggestions on improving the code!

• Mast: Please tell us more about the purpose of the code. It's a timer, ok, timing what? What is it supposed to do? What prompted you to write this?
• user214772: It doesn't have any special purpose. It was just for fun. I know that this answer doesn't really help, but I can't give a better one.
• markspace: I don't like global imports: javax.swing.* I can't tell what sort of Timer you have. There's java.util.Timer and java.swing.Timer, and it isn't obvious which one you're using. Please don't use global imports like this.
• user33306: @markspace - I would say the difference between java.util and javax.swing is pretty easy to see, especially when only one of them is being imported. Also, as in this case, it seems to me that using a global is better than adding a lot of extra lines to the imports

Answer 1

A few things I noticed:

Quite a few of your variables can be marked final. From my understanding pretty much any variable where the underlying object doesn't get reassigned to a new object.

Instead of 3 separate variable for the time parts, you could use java.time.LocalTime to hold the time parts. Not only does this reduce your code, but it simplifies the count down portion in that subtracting 1 second will adjust the other fields automatically.

Since Integer.valueOf uses Integer.parseInt anyway, I think it would be better, in this case, to use Integer.parseInt

You misspelled the title of the message dialog when the countdown is done.

I think INFORMATION_MESSAGE is a better icon, for the message dialog, than CANCEL_OPTION, in this case.

The throws clause in the main declaration is redundant.

With these adjustments your code could look like this:

import javax.swing.*;
import javax.swing.text.NumberFormatter;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.text.NumberFormat;
import java.time.LocalTime;
import static javax.swing.WindowConstants.EXIT_ON_CLOSE;
public class Counter {
 private final JButton button;
 private final JFormattedTextField hours;
 private final JFormattedTextField minutes;
 private final JFormattedTextField seconds;
 private final Timer timer;
 private final int delay = 1000;
 private final ActionListener taskPerformer = new ActionListener() {
 public void actionPerformed(ActionEvent evt) {
 time = time.minusSeconds(1);
 if (time.equals(LocalTime.MIN)) {
 Toolkit.getDefaultToolkit().beep();
 JOptionPane.showMessageDialog(null, "Countdown ended!", "Ended", JOptionPane.INFORMATION_MESSAGE);
 timer.stop(); 
 }
 seconds.setText(String.valueOf(time.getSecond()));
 minutes.setText(String.valueOf(time.getMinute()));
 hours.setText(String.valueOf(time.getHour()));
 }
 };
 private LocalTime time = LocalTime.of(0, 0, 0);
 public static void main(String[] args) {
 SwingUtilities.invokeLater(Counter::new);
 }
 Counter() {
 timer = new Timer(delay,taskPerformer);
 JFrame frame = new JFrame();
 frame.setSize(300, 200);
 frame.setDefaultCloseOperation(EXIT_ON_CLOSE);
 JPanel panel = new JPanel(new BorderLayout());
 JPanel subPanel1 = new JPanel(new GridLayout(2, 3));
 /*
 * The following lines ensure that the user can
 * only enter numbers.
 */
 NumberFormat format = NumberFormat.getInstance();
 NumberFormatter formatter = new NumberFormatter(format);
 formatter.setValueClass(Integer.class);
 formatter.setMinimum(0);
 formatter.setMaximum(Integer.MAX_VALUE);
 formatter.setAllowsInvalid(false);
 formatter.setCommitsOnValidEdit(true);
 //"labeling"
 JTextField text1 = new JTextField();
 text1.setText("hours:");
 text1.setEditable(false);
 JTextField text2 = new JTextField();
 text2.setText("minutes:");
 text2.setEditable(false);
 JTextField text3 = new JTextField();
 text3.setText("seconds:");
 text3.setEditable(false);
 //fields for minutes and seconds
 hours = new JFormattedTextField(formatter);
 minutes = new JFormattedTextField(formatter);
 seconds = new JFormattedTextField(formatter);
 hours.setText("0");
 minutes.setText("0");
 seconds.setText("0");
 JPanel subPanel2 = new JPanel();
 /*
 * When the user presses the OK-button, the program will
 * start to count down.
 */
 button = new JButton("OK");
 button.addActionListener(actionEvent -> {
 time = LocalTime.of(Integer.parseInt(hours.getText()), Integer.parseInt(minutes.getText()), Integer.parseInt(seconds.getText()));
 button.setEnabled(false);
 //Timer for one second delay
 timer.start();
 });
 //Reset-button
 JButton button2 = new JButton("Reset");
 button2.addActionListener(actionEvent -> {
 hours.setText("0");
 minutes.setText("0");
 seconds.setText("0");
 button.setEnabled(true);
 time = LocalTime.of(0, 0, 0);
 timer.stop();
 });
 subPanel1.add(text1);
 subPanel1.add(text2);
 subPanel1.add(text3);
 subPanel1.add(hours);
 subPanel1.add(minutes);
 subPanel1.add(seconds);
 subPanel2.add(button);
 subPanel2.add(button2);
 panel.add(subPanel1, BorderLayout.CENTER);
 panel.add(subPanel2, BorderLayout.PAGE_END);
 frame.add(panel);
 frame.setVisible(true);
 }
}

• Martin Frank: would you please rename the magic number delay = 1000?