GUI Update and Threads

Question

Hello all, I'm new to Java and am having a hard time trying to understand how to implement multi-threading. I've built a simple app with GUI for converting files between encodings. The program works fine but some files take a long time to convert so I want to show the user some status text in the GUI. The conversion function is called from within a button click event, and further from within a loop that cycles through a directory of files to convert. I'm trying to show the name of the file being converted in a label in the GUI, but the label won't update until the button click event finishes, so only the last file converted is displayed.
I've read through countless examples on this forum and others, and in several online books. I understand the concept of multi-threading and some of the issues surrounding them, but can't seem to grasp the mechanics of getting them set up in code at this point.
Can anyone provide some coding tips? The code is provided below minus the NetBeans generated layout code. I can provide this also if needed. You'll see some lines commented out in the For loop that I tried but that didn't work.
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.io.*;
public class EnCon4 extends javax.swing.JFrame {
    //Declare variables and set default values
    String fname="UTF-16";
    String tname="UTF8";
    String infile;
    String outfile;
    /** Creates new form EnCon4 */
    public EnCon4() {
        initComponents();
    private void encodingToListActionPerformed(java.awt.event.ActionEvent evt) {                                              
        tname=(String)encodingToList.getSelectedItem();
    private void encodingFromListActionPerformed(java.awt.event.ActionEvent evt) {                                                
        fname=(String)encodingFromList.getSelectedItem();
    private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                        
        jLabelStatus.setText("Converting From: " + fname + "  To: " + tname);
        jLabelStatus.repaint();
     File dir1 = new File ("."); //Set current directory
     //Create new subdirectory for converted files
     String newDirName = dir1 + File.separator + "Conv"; 
         File dir2 = new File(newDirName);
         if (!dir2.exists()) {
            dir2.mkdir();
         try {
            //Set path to current directory
            File pathName = new File(dir1.getCanonicalPath());
            File[] contents = pathName.listFiles();
            for (File file : contents) {
                if (!file.isDirectory()) {
                    //Create the converted files
                //Set variables
                infile = dir1.getCanonicalPath() + File.separator + file.getName();
                outfile = dir2.getCanonicalPath() + File.separator + file.getName();
                //Check file names to exclude converting the java class file
                if (!infile.endsWith("class") & !infile.endsWith("jar")) {
                        //Print the file name
                        jLabelStatus.setText("Converting file:  " + file.getName());
                        jLabelStatus.repaint();
                        //catch (Exception econ) {
                        //    System.out.print(econ.getMessage());
                        //    System.exit(1);
                        //System.out.println(file.getName());
                   //Call conversion function in a new thread.
                   //Example with static args //try { convert("NamesASCII.txt", "UTF8.txt", "ISO8859_1", "UTF8"); }
                       //Thread t = new Thread(new Runnable() {
                            //public void run() {
                            try {convert(infile, outfile, fname, tname);
                            catch (Exception econ) {
                                jLabelStatus.setText(econ.getMessage());
                                jLabelStatus.repaint();
                                //System.out.print(econ.getMessage());
                             //System.exit(1);
                        //t.start();
            //jLabelStatus.setText("Conversion complete.");
            //jLabelStatus.repaint();
         catch(IOException econ) {
            jLabelStatus.setText("Error: " + econ);
            //System.out.println("Error: " + econ);
    public static void convert(String infile, String outfile, String from, String to)
        throws IOException, UnsupportedEncodingException {
        // set up byte streams
        InputStream in;
        if (infile != null) in = new FileInputStream(infile);
        else in = System.in;
        OutputStream out;
        if (outfile != null) out = new FileOutputStream(outfile);
        else out = System.out;
        // Set up character stream
        Reader r = new BufferedReader(new InputStreamReader(in, from));
        Writer w = new BufferedWriter(new OutputStreamWriter(out, to));
        // Copy characters from input to output.  The InputStreamReader
        // converts from the input encoding to Unicode, and the OutputStreamWriter
        // converts from Unicode to the output encoding.  Characters that cannot be
        // represented in the output encoding are output as '?'
        char[] buffer = new char[4096];
        int len;
        while((len = r.read(buffer)) != -1)
          w.write(buffer, 0, len);
        r.close();
        w.flush();
        w.close();
    public static void main(String args[]) {
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new EnCon4().setVisible(true);
    // Variables declaration - do not modify                    
    private javax.swing.JComboBox encodingFromList;
    private javax.swing.JComboBox encodingToList;
    private javax.swing.JButton jButton1;
    private javax.swing.JLabel jLabel1;
    private javax.swing.JLabel jLabel2;
    private javax.swing.JLabel jLabel3;
    private javax.swing.JLabel jLabelStatus;
    private javax.swing.JPanel jPanel1;
    // End of variables declaration                  
}

Answer 1

There are two key principles here. The first is "remove long-running
processes from the event dispatch thread". If in doubt, you
can check with SwingUtilities.isEventDIspatch(). The second is
"put GUI updates on the event dispatch thread", preferable
with SwingUtilities.invokeLater().
Today is my last day at work, so here's a fish:
import java.awt.event.*;
import java.io.*;
import javax.swing.*;
public class EnCon extends JFrame{
    String fname="UTF-16";
    String tname="UTF8";
    String infile;
    String outfile;
    /** Creates new form EnCon4 */
    public EnCon() {
        super("EnCon");
        jButton1.addActionListener(new ActionListener() {
            public void actionPerformed(final ActionEvent ae) {
                final Thread t = new Thread(new MyRunner());
                t.start();
        final JPanel container = new JPanel();
        container.add(jButton1);
        container.add(jLabelStatus);
        this.getContentPane().add(container);
        this.pack();
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    private class MyRunner implements Runnable {
        public void run() {
            sendMessage("Converting From: " + fname + "  To: " + tname);
            File dir1 = new File ("."); //Set current directory
            //Create new subdirectory for converted files
            String newDirName = dir1 + File.separator + "Conv";
            File dir2 = new File(newDirName);
            if (!dir2.exists()) {
                dir2.mkdir();
            try {
                //Set path to current directory
                File pathName = new File(dir1.getCanonicalPath());
                File[] contents = pathName.listFiles();
                for (File file : contents) {
                    if (!file.isDirectory()) {
                        infile = dir1.getCanonicalPath() + File.separator + file.getName();
                        outfile = dir2.getCanonicalPath() + File.separator + file.getName();
                        if (!infile.endsWith("class") & !infile.endsWith("jar")) {
                            sendMessage("Converting file:  " + file.getName());
                            try {
                                convert(infile, outfile, fname, tname);
                                sendMessage("Done");
                            catch (Exception econ) {
                                sendMessage(econ.getMessage());
            catch(IOException econ) {
                sendMessage("Error: " + econ);
        private void sendMessage(final String message) {
            SwingUtilities.invokeLater(new Runnable() {
                public void run() {
                    jLabelStatus.setText(message);
    public static void convert(String infile, String outfile, String from, String to)
    throws IOException, UnsupportedEncodingException {
        // set up byte streams
        InputStream in;
        if (infile != null) in = new FileInputStream(infile);
        else in = System.in;
        OutputStream out;
        if (outfile != null) out = new FileOutputStream(outfile);
        else out = System.out;
        // Set up character stream
        Reader r = new BufferedReader(new InputStreamReader(in, from));
        Writer w = new BufferedWriter(new OutputStreamWriter(out, to));
        // Copy characters from input to output.  The InputStreamReader
        // converts from the input encoding to Unicode, and the OutputStreamWriter
        // converts from Unicode to the output encoding.  Characters that cannot be
        // represented in the output encoding are output as '?'
        char[] buffer = new char[4096];
        int len;
        while((len = r.read(buffer)) != -1)
            w.write(buffer, 0, len);
        r.close();
        w.flush();
        w.close();
    public static void main(String args[]) {
        new EnCon().setVisible(true);
    // Variables declaration - do not modify
    private JButton jButton1 = new JButton("Convert");
    private JLabel jLabelStatus = new JLabel("jLabelStatus");
    // End of variables declaration
}