Question

I am trying to create a simple GUI form which has only 2 elements – a simple label and a button. The text displayed on button is ‘Start’. The label is displaying 0 by default.

When I click Start button following actions shall take place:

1. Counter shall start incrementing by 1 from 0 at every 1 second.
2. Text displayed on the Start button shall change to Stop.
3. When again I click on the same button (now showing caption as Stop), increment shall stop.
4. Text on the button shall change to Start. And so on…

I am developing my application in Netbeans.

As shown in the above diagram, there are 2 .java files

Contents of AGC.java are:

public class AGC extends javax.swing.JFrame 
{
    public AGC()
    {    
        initComponents();
    }

    public static void main(String args[])
    {
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() 
            {
                new AGC().setVisible(true);
            }
        });
    }

    private javax.swing.JButton btnStartStop;  // name of start stop button
    private javax.swing.JLabel lblCounter;   // name of the label

}

Contents of Main.java are:

public class Main 
{
    public static int count = 0;
    public static boolean started = false;
}

I want to implement following logic:

private void btnStartStopMouseClicked(java.awt.event.MouseEvent evt) 
{
    if (Main.stared == true)
    {
        // logic to start counting
    }
    else
    {
        // logic to stop counting
    }
}

My problem is this:

1. How to update lblCounter at every 1 second?
2. What logic shall I implement to start the timer of 1 second and how to access lblCounter in that method ?

Kindly help. A working code would be very highly appreciated. Thanks in advance.

Jay

Answer 1

Simply use a javax.swing.Timer, and make one ActionListener, to do this thing for you . Give me ten mins for a working code example 🙂

Here is a sample program for further help :

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

public class UpdateWithTimer extends JFrame
{
    private Timer timer;
    private JButton startStopButton;
    private JLabel changingLabel;
    private int counter = 0;
    private boolean flag = false;
    private ActionListener timerAction = new ActionListener()
    {
        public void actionPerformed(ActionEvent ae)
        {
            counter++;
            changingLabel.setText("" + counter);
        }
    };

    private ActionListener buttonAction = new ActionListener()  
    {
        public void actionPerformed(ActionEvent ae)
        {
            if (!flag)
            {
                startStopButton.setText("STOP TIMER");
                timer.start();
                flag = true;
            }
            else if (flag)
            {
                startStopButton.setText("START TIMER");
                timer.stop();
                flag = false;
            }
        }
    };

    private void createAndDisplayGUI()
    {
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLocationByPlatform(true);

        JPanel contentPane = new JPanel();
        changingLabel = new JLabel("" + counter);
        contentPane.add(changingLabel);

        startStopButton = new JButton("START TIMER");
        startStopButton.addActionListener(buttonAction);

        add(contentPane, BorderLayout.CENTER);
        add(startStopButton, BorderLayout.PAGE_END);

        timer = new Timer(1000, timerAction);

        setSize(300, 300);
        setVisible(true);
    }

    public static void main(String... args)
    {
        SwingUtilities.invokeLater(new Runnable()
        {
            public void run()
            {
                new UpdateWithTimer().createAndDisplayGUI();
            }
        });
    }
}

If you want the counter to again revert back to 0, on Stopping the Timer, simply add

else if (flag)
{
    startStopButton.setText("START TIMER");
    timer.stop();
    flag = false;
    counter = 0;
    changingLabel.setText("" + counter);
}

this part to the buttonAction‘s actionPerformed(...) method.