How to update Text Field created with NetBeans graphical GUI designer in Java

Question

I've been writing embedded C code for decades and I'm looking to update my skill set by learning Java.

I also have a need for a graphical test tool for a project (read serial port, process data, write result to serial port based on GUI button selections, etc)

I'm trying to use NetBeans graphical GUI designer to create the GUI and then add Java code to implement the logic but I'm still learning Java so I'm not sure how to access the text field in my GUI from the Java code. Specifically I want a on screen text box that updates every second with the current time (this will eventually become a health check routing looking for missed command timeouts, etc).

The problem I'm having is how to access the text field object called timeDisplayField from my healthCheck() routine. The healthCheck() routine is getting called every second but when I uncomment any attempt at getting to the timeDisplayField object I either get a compile error or a NullPointer run time error.

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */

package myPackage;

import java.util.Calendar;
import java.util.Timer;
import java.util.TimerTask;
import java.util.Date;

/**
 *
 * @author SGrunza
 */


public class mainWindow extends javax.swing.JFrame {

    /**
     * Creates new form mainWindow
     */



        public void healthCheck()
{
    Calendar    now = Calendar.getInstance();
    int         hour = now.get( Calendar.HOUR_OF_DAY );
    int         minute = now.get( Calendar.MINUTE );
    int         second = now.get( Calendar.SECOND );

    String      timeString = new String();

    //System.out.printf("%02d:%02d:%02d\r\n", hour, minute, second );

    timeString = timeString.format( "%02d:%02d:%02d\r\n", hour, minute, second );
    timeDisplayField.setText( timeString );
}

    public mainWindow() 
    {
        Timer       healthTimer = new Timer();

        healthTimer.scheduleAtFixedRate( new TimerTask()
                {
                    @Override 
                    public void run()
                {
                    //System.out.println( "healthTask " + new Date() +
                    //        "Thread name: " + Thread.currentThread().getName() );
                    healthCheck();
                }
                },
                0,  // delay until first run
                1000 ); // delay for each subsequent run


        initComponents();
    }

    /**
     * This method is called from within the constructor to initialize the form.
     * WARNING: Do NOT modify this code. The content of this method is always
     * regenerated by the Form Editor.
     */
    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">//GEN-BEGIN:initComponents
    private void initComponents() {

        interfaceTypeGroup = new javax.swing.ButtonGroup();
        jPanel1 = new javax.swing.JPanel();
        nfcButton = new javax.swing.JRadioButton();
        smipButton = new javax.swing.JRadioButton();
        serialButton = new javax.swing.JRadioButton();
        appStatusField = new javax.swing.JTextField();
        msgField = new javax.swing.JTextField();
        cardReaderStatusField = new javax.swing.JTextField();
        timeDisplayField = new javax.swing.JTextField();
        activateButton = new javax.swing.JButton();
        readButton = new javax.swing.JButton();
        deactivateButton = new javax.swing.JButton();
        checkSleepButton = new javax.swing.JButton();
        getInfoButton = new javax.swing.JButton();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

        interfaceTypeGroup.add(nfcButton);
        nfcButton.setSelected(true);
        nfcButton.setText("NFC");

        interfaceTypeGroup.add(smipButton);
        smipButton.setForeground(new java.awt.Color(153, 153, 153));
        smipButton.setText("SMIP");

        interfaceTypeGroup.add(serialButton);
        serialButton.setForeground(new java.awt.Color(153, 153, 153));
        serialButton.setText("Serial");

        appStatusField.setText("appStatus");

        msgField.setText("msgWindow");

        cardReaderStatusField.setText("cardReader_status");

        timeDisplayField.setText("timeDisplay");

        activateButton.setLabel("Activate");

        readButton.setText("Read Sensor");

        deactivateButton.setText("Deactivate");

        checkSleepButton.setText("Check Sleep");

        getInfoButton.setText("Get Info");

        javax.swing.GroupLayout jPanel1Layout = new javax.swing.GroupLayout(jPanel1);
        jPanel1.setLayout(jPanel1Layout);
        jPanel1Layout.setHorizontalGroup(
            jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, jPanel1Layout.createSequentialGroup()
                .addContainerGap()
                .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                    .addComponent(msgField)
                    .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.TRAILING, false)
                        .addComponent(activateButton, javax.swing.GroupLayout.Alignment.LEADING, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                        .addComponent(deactivateButton, javax.swing.GroupLayout.Alignment.LEADING, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                        .addComponent(readButton, javax.swing.GroupLayout.Alignment.LEADING, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)))
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING, false)
                    .addGroup(jPanel1Layout.createSequentialGroup()
                        .addComponent(getInfoButton, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                        .addContainerGap())
                    .addGroup(jPanel1Layout.createSequentialGroup()
                        .addComponent(checkSleepButton, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                        .addGap(12, 12, 12))))
            .addGroup(jPanel1Layout.createSequentialGroup()
                .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                    .addGroup(jPanel1Layout.createSequentialGroup()
                        .addGap(12, 12, 12)
                        .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                            .addComponent(nfcButton)
                            .addComponent(smipButton)
                            .addComponent(serialButton))
                        .addGap(18, 18, 18)
                        .addComponent(cardReaderStatusField))
                    .addGroup(jPanel1Layout.createSequentialGroup()
                        .addGap(12, 12, 12)
                        .addComponent(appStatusField, javax.swing.GroupLayout.PREFERRED_SIZE, 203, javax.swing.GroupLayout.PREFERRED_SIZE)
                        .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, 564, Short.MAX_VALUE)
                        .addComponent(timeDisplayField, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)))
                .addGap(12, 12, 12))
        );
        jPanel1Layout.setVerticalGroup(
            jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(jPanel1Layout.createSequentialGroup()
                .addContainerGap()
                .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING, false)
                    .addGroup(jPanel1Layout.createSequentialGroup()
                        .addComponent(nfcButton)
                        .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
                        .addComponent(smipButton)
                        .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
                        .addComponent(serialButton))
                    .addComponent(cardReaderStatusField))
                .addGap(18, 18, 18)
                .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                    .addComponent(timeDisplayField, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                    .addComponent(appStatusField, javax.swing.GroupLayout.PREFERRED_SIZE, 63, javax.swing.GroupLayout.PREFERRED_SIZE))
                .addGap(18, 18, 18)
                .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                    .addComponent(activateButton)
                    .addComponent(getInfoButton))
                .addGap(18, 18, 18)
                .addComponent(readButton)
                .addGap(18, 18, 18)
                .addComponent(deactivateButton)
                .addGap(37, 37, 37)
                .addComponent(checkSleepButton)
                .addGap(18, 18, 18)
                .addComponent(msgField, javax.swing.GroupLayout.DEFAULT_SIZE, 217, Short.MAX_VALUE)
                .addContainerGap())
        );

        timeDisplayField.getAccessibleContext().setAccessibleName("timeDisplayField");

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addComponent(jPanel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                .addContainerGap())
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addComponent(jPanel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
        );

        pack();
    }// </editor-fold>//GEN-END:initComponents

    /**
     * @param args the command line arguments
     */
    public static void main(String args[]) {
        /* Set the Nimbus look and feel */
        //<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
        /* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel.
         * For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html 
         */
        try {
            for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
                if ("Nimbus".equals(info.getName())) {
                    javax.swing.UIManager.setLookAndFeel(info.getClassName());
                    break;
                }
            }
        } catch (ClassNotFoundException ex) {
            java.util.logging.Logger.getLogger(mainWindow.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (InstantiationException ex) {
            java.util.logging.Logger.getLogger(mainWindow.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            java.util.logging.Logger.getLogger(mainWindow.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (javax.swing.UnsupportedLookAndFeelException ex) {
            java.util.logging.Logger.getLogger(mainWindow.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        }
        //</editor-fold>

        /* Create and display the form */
        java.awt.EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                new mainWindow().setVisible(true);
            }
        });
    }


    // Variables declaration - do not modify//GEN-BEGIN:variables
    public javax.swing.JButton activateButton;
    public javax.swing.JTextField appStatusField;
    public javax.swing.JTextField cardReaderStatusField;
    public javax.swing.JButton checkSleepButton;
    public javax.swing.JButton deactivateButton;
    public javax.swing.JButton getInfoButton;
    public javax.swing.ButtonGroup interfaceTypeGroup;
    public javax.swing.JPanel jPanel1;
    public javax.swing.JTextField msgField;
    public javax.swing.JRadioButton nfcButton;
    public javax.swing.JButton readButton;
    public javax.swing.JRadioButton serialButton;
    public javax.swing.JRadioButton smipButton;
    public javax.swing.JTextField timeDisplayField;
    // End of variables declaration//GEN-END:variables
}

I'm new enough to Java that I'm not sure where to look for help. I suspect part of the problem is in using the NetBeans GUI builder but I really don't want to build all the GUI by hand.

To boil this down to a simple question: How do I change healthCheck() so that it updates the text field on the screen?

For better help always post the entire error message (stacktrace) and mark with a comment the line that throws it. — c0der, Apr 08 '20 at 08:03

score 1 · Accepted Answer · answered Apr 08 '20 at 07:38

The answer is in What is a NullPointerException and how do i fix it. You can see it in the stacktrace (error):

Exception in thread "Timer-0" java.lang.NullPointerException
    at rae.mainWindow.healthCheck(mainWindow.java:24)
    at rae.mainWindow$1.run(mainWindow.java:35)
    at java.util.TimerThread.mainLoop(Timer.java:555)
    at java.util.TimerThread.run(Timer.java:505)

In line 24, you have this line:

timeDisplayField.setText(timeString);

timeString is not null which means timeDisplayField is null. That's because you first start the timer and after you call initComponents method which creates the textfield:

public mainWindow() {
    Timer healthTimer = new Timer();

    healthTimer.scheduleAtFixedRate(new TimerTask() {
        @Override
        public void run() {
            // System.out.println( "healthTask " + new Date() +
            // "Thread name: " + Thread.currentThread().getName() );
            healthCheck();
        }
    }, 0, // delay until first run
            1000); // delay for each subsequent run

    initComponents(); //here
}

You can fix it by calling initComponents before time initiation:

public mainWindow() {
    Timer healthTimer = new Timer();

    initComponents(); //Before timer

    healthTimer.scheduleAtFixedRate(new TimerTask() {
        @Override
        public void run() {
            // System.out.println( "healthTask " + new Date() +
            // "Thread name: " + Thread.currentThread().getName() );
            healthCheck();
        }
    }, 0, // delay until first run
            1000); // delay for each subsequent run

}

However, using java.util.Timer is not recommended in a Swing environment. Consider changing it to a Swing Timer which is created for such cases. A good example of its usage can be found in this post.

As you recommended, it might be beneficial to use Swing Timer in your answer. +1 — c0der, Apr 08 '20 at 08:00

How to update Text Field created with NetBeans graphical GUI designer in Java

1 Answers1