Continually set JTextArea text within ActionListener

Question

I am trying to create a button that, when pressed, will display text in a JTextArea, continually updating every time a step in the loop is run after a wait period. The code I have now prints what it would look look like on the first step of the loop, then stops. The action I am referring to is at the bottom under //Actions.

public class MainWindow {

    private JFrame frmMcakennaAntivirus;

    /**
     * Launch the application.
     */
    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    MainWindow window = new MainWindow();
                    window.frmMcakennaAntivirus.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    /**
     * Create the application.
     */
    public MainWindow() {
        initialize();
    }

    /**
     * Initialize the contents of the frame.
     */
    private void initialize() {
        frmMcakennaAntivirus = new JFrame();
        frmMcakennaAntivirus.setResizable(false);
        frmMcakennaAntivirus.setTitle("McAkenna Anti-Virus");
        frmMcakennaAntivirus.setAlwaysOnTop(true);
        frmMcakennaAntivirus.setBounds(100, 100, 303, 197);
        frmMcakennaAntivirus.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        GridBagLayout gridBagLayout = new GridBagLayout();
        gridBagLayout.columnWidths = new int[]{0, 149, 135, 0, 0};
        gridBagLayout.rowHeights = new int[]{0, 14, 0, 24, 45, 0, 0};
        gridBagLayout.columnWeights = new double[]{0.0, 0.0, 0.0, 0.0, Double.MIN_VALUE};
        gridBagLayout.rowWeights = new double[]{0.0, 0.0, 0.0, 0.0, 0.0, 0.0, Double.MIN_VALUE};
        frmMcakennaAntivirus.getContentPane().setLayout(gridBagLayout);

        JSeparator separator = new JSeparator();
        GridBagConstraints gbc_separator = new GridBagConstraints();
        gbc_separator.insets = new Insets(0, 0, 5, 5);
        gbc_separator.gridx = 1;
        gbc_separator.gridy = 0;
        frmMcakennaAntivirus.getContentPane().add(separator, gbc_separator);

        JSeparator separator_1 = new JSeparator();
        GridBagConstraints gbc_separator_1 = new GridBagConstraints();
        gbc_separator_1.insets = new Insets(0, 0, 5, 5);
        gbc_separator_1.gridx = 0;
        gbc_separator_1.gridy = 1;
        frmMcakennaAntivirus.getContentPane().add(separator_1, gbc_separator_1);

        JButton btnBeginScan = new JButton("Begin Scan");
        btnBeginScan.setFont(new Font("Tahoma", Font.BOLD, 11));
        btnBeginScan.setForeground(new Color(0, 0, 0));
        btnBeginScan.setBackground(new Color(124, 252, 0));
        GridBagConstraints gbc_btnBeginScan = new GridBagConstraints();
        gbc_btnBeginScan.insets = new Insets(0, 0, 5, 5);
        gbc_btnBeginScan.gridx = 1;
        gbc_btnBeginScan.gridy = 1;
        frmMcakennaAntivirus.getContentPane().add(btnBeginScan, gbc_btnBeginScan);

        JButton btnFixProblems = new JButton("Fix Problems");
        btnFixProblems.setBackground(new Color(127, 255, 0));
        GridBagConstraints gbc_btnFixProblems = new GridBagConstraints();
        gbc_btnFixProblems.insets = new Insets(0, 0, 5, 5);
        gbc_btnFixProblems.gridx = 2;
        gbc_btnFixProblems.gridy = 1;
        frmMcakennaAntivirus.getContentPane().add(btnFixProblems, gbc_btnFixProblems);

        JSeparator separator_2 = new JSeparator();
        GridBagConstraints gbc_separator_2 = new GridBagConstraints();
        gbc_separator_2.insets = new Insets(0, 0, 5, 0);
        gbc_separator_2.gridx = 3;
        gbc_separator_2.gridy = 1;
        frmMcakennaAntivirus.getContentPane().add(separator_2, gbc_separator_2);

        Choice choice = new Choice();
        choice.setBackground(SystemColor.scrollbar);
        GridBagConstraints gbc_choice = new GridBagConstraints();
        gbc_choice.insets = new Insets(0, 0, 5, 5);
        gbc_choice.fill = GridBagConstraints.HORIZONTAL;
        gbc_choice.gridx = 1;
        gbc_choice.gridy = 2;
        frmMcakennaAntivirus.getContentPane().add(choice, gbc_choice);
        choice.add("Full System Scan");
        choice.add("Quick Scan");

        JProgressBar progressBar = new JProgressBar();
        GridBagConstraints gbc_progressBar = new GridBagConstraints();
        gbc_progressBar.fill = GridBagConstraints.BOTH;
        gbc_progressBar.insets = new Insets(0, 0, 5, 5);
        gbc_progressBar.gridx = 1;
        gbc_progressBar.gridy = 3;
        frmMcakennaAntivirus.getContentPane().add(progressBar, gbc_progressBar);

        final JTextArea textArea = new JTextArea();
        textArea.setLineWrap(true);
        textArea.setFont(new Font("Source Sans Pro Light", Font.PLAIN, 12));
        textArea.setEditable(false);
        textArea.setBackground(SystemColor.inactiveCaption);
        GridBagConstraints gbc_textArea = new GridBagConstraints();
        gbc_textArea.insets = new Insets(0, 0, 5, 5);
        gbc_textArea.fill = GridBagConstraints.BOTH;
        gbc_textArea.gridx = 1;
        gbc_textArea.gridy = 4;
        frmMcakennaAntivirus.getContentPane().add(textArea, gbc_textArea);

        JButton btnCancelScan = new JButton("Cancel Scan");
        btnCancelScan.setBackground(new Color(255, 0, 0));
        GridBagConstraints gbc_btnCancelScan = new GridBagConstraints();
        gbc_btnCancelScan.insets = new Insets(0, 0, 0, 5);
        gbc_btnCancelScan.gridx = 1;
        gbc_btnCancelScan.gridy = 5;
        frmMcakennaAntivirus.getContentPane().add(btnCancelScan, gbc_btnCancelScan);



        //Actions

        btnBeginScan.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {

                for (int x= 1; x < 6735; x++){
                    textArea.setText("Files scanned: " + x + "\nViruses found: " + x/350);
                    try {
                        Thread.sleep(randInt(90, 200));
                    } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                }

            }
        });

    }

    public static int randInt(int min, int max) {

        Random rand = null;

        int randomNum = rand.nextInt((max - min) + 1) + min;

        return randomNum;
    }

}

Answer 1

You're blocking the Event Dispatching Thread, which is responsible for, among other things, processing repaint requests.

Swing is a single threaded frame, you should never run long running or blocking operations from within the context of the EDT.

See Concurrency in Swing for more details

Use a SwingWorker or Swing Timer instead.

See Worker Threads and SwingWorker and How to use Swing Timers for more details

As a side note, you're also going to encounter a NullPointerException...

Random rand = null;
int randomNum = rand.nextInt((max - min) + 1) + min;

When using Random, you should create a single instance and re-use for as long as you need it. This will ensure that the values you get from it are properly (as best as it can) randomised, otherwise you may end up with repeating values in a very short period of time