swing - Java frame not displaying properly during a while loop

Question

Here's a serious issue im having with a jFrame. I have one "Main Frame" where everything is done from, however i have another frame with a gif image in it (Loading, that circle that goes round and round), that is used as a splash screen saying "Processing, Please wait", however when i pull through that frame and my while loop runs, the frame goes blank and nothing displays until after the loop.

I am assuming that this is due to the while loop consuming computer resources and "blocking" any other process from running.

Please advise on what i should do.

the code for declaring the new frame is standard but i will post it anyway below.

Processing nc = new Processing();
nc.setVisible(true);

Here is my full code so you can see what im trying t achieve:

Code from frame 1 (Excel Extractor):

Processing nc = new Processing();
    nc.setVisible(true);

    JFileChooser chooser = new JFileChooser();
    chooser.setFileSelectionMode(JFileChooser.DIRECTORIES_ONLY);
    int option = chooser.showOpenDialog(this); // parentComponent must a component like JFrame, JDialog...
    if (option == JFileChooser.APPROVE_OPTION) {
    File selectedFile = chooser.getSelectedFile();
     directory = selectedFile.getAbsolutePath();
     System.out.println(directory);

    }


   //create a input stream for your excel file from which data will be read. 
   DateFormat dateFormat = new SimpleDateFormat("yyyy_MM_dd");
   SimpleDateFormat sdf = new SimpleDateFormat("HHmmss");
   String curdate = dateFormat.format(new Date());
   Calendar cal = Calendar.getInstance();
   cal.getTime();
   String curtime = sdf.format(cal.getTime());
try{

FileInputStream excelSheetInput = new FileInputStream(path);
//POIFSFileSystem myFileSystem = new POIFSFileSystem(excelSheetInput);
    XSSFWorkbook myWorkBook = new XSSFWorkbook(excelSheetInput);
    //get first work sheet in your excel file.
    Sheet sheet = myWorkBook.getSheetAt(0);
    //we will read data in first rows(0) second column(1)
    Iterator<Row> rowIterator = sheet.iterator();
    Row myRow1 = sheet.getRow(0);
    Cell myCell1 = myRow1.getCell(0);
    String header="";
    Iterator<Cell> cellIterator1 = myRow1.cellIterator();
    int rowCount = 0;

    while(cellIterator1.hasNext()) {

                            Cell cell1 = cellIterator1.next();

                            switch(cell1.getCellType()) {
                                case Cell.CELL_TYPE_BOOLEAN:
                                    header = header + """+cell1.getBooleanCellValue()+""" + ",";
                                    break;
                                case Cell.CELL_TYPE_NUMERIC:
                                    cell1.setCellType(Cell.CELL_TYPE_STRING);
                                     header = header + """+cell1.getStringCellValue()+"""+",";
                                    //System.out.print(cell.getStringCellValue() + "");
                                    break;
                                case Cell.CELL_TYPE_STRING:
                                    header = header + """+cell1.getStringCellValue()+"""+",";
                                    //System.out.print(cell.getStringCellValue() + "");
                                    break;
                            }
    }

    Row myRow = sheet.getRow(1);
    Cell myCell= myRow.getCell(0);
    Iterator<Cell> cellIterator;
    String firstCell = myCell.getStringCellValue();
    int count =1;
    String nextCell;
    String Matter = "Matter Number: "+firstCell;
    String num = firstCell;
    System.out.println(Matter);
    fWriter = new FileWriter(new File(directory, num+"_"+curdate+"_"+curtime+".csv"));
    writer = new BufferedWriter(fWriter);
    writer.write(Matter);
    writer.newLine();
    writer.write(header);
    writer.newLine();
    String temp;
    while(rowIterator.hasNext())
    {


        //temp = "" + rowCount;
        //jLabel5.setText(temp);
        myRow = sheet.getRow(count);
        cellIterator = myRow.cellIterator();
        Cell myCell2 = myRow.getCell(0);
        nextCell= myCell2.getStringCellValue();


        if(nextCell.equals(firstCell))
        {

            while(cellIterator.hasNext()) {

                            Cell cell = cellIterator.next();

                            switch(cell.getCellType()) {
                                case Cell.CELL_TYPE_BOOLEAN:
                                    System.out.print(cell.getBooleanCellValue() + "");
                                    break;
                                case Cell.CELL_TYPE_NUMERIC:
                                    cell.setCellType(Cell.CELL_TYPE_STRING);

                                     System.out.print(cell.getStringCellValue()+",");

                                    //System.out.print(cell.getStringCellValue() + "");
                                    writer.write(cell.getStringCellValue()+",");
                                    break;
                                case Cell.CELL_TYPE_STRING:
                                    System.out.print(cell.getStringCellValue()+",");
                                    //System.out.print(cell.getStringCellValue() + "");
                                    writer.write(cell.getStringCellValue()+",");
                                    break;
                            }
                        }
            System.out.println();
            writer.newLine();
            count++;
            rowCount++;



        }
        else
        {          

            writer.close();
            myRow = sheet.getRow(count);
            myCell2= myRow.getCell(0);
            nextCell=myCell2.getStringCellValue();
            firstCell=nextCell;
            Matter = "Matter Number: "+firstCell;
            num = firstCell;
            System.out.println(Matter);
            fWriter = new FileWriter(new File(directory, num+"_"+curdate+"_"+curtime+".csv"));
            writer = new BufferedWriter(fWriter);
            writer.write(Matter);
            writer.newLine();
            writer.write(header);
            writer.newLine();
        }


    }
}
catch (Exception e)
{
}

  try {
    nc.dispose();
    writer.close();
} catch (IOException ex) {
    Logger.getLogger(FileChooser.class.getName()).log(Level.SEVERE, null, ex);
}
}

The second frames code (Processing):

private void initComponents() {

    jLabel1 = new javax.swing.JLabel();
    jLabel2 = new javax.swing.JLabel();

    setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

    jLabel1.setFont(new java.awt.Font("Tahoma", 1, 14)); // NOI18N
    jLabel1.setText("Processing, Please Wait...");

    jLabel2.setHorizontalAlignment(javax.swing.SwingConstants.CENTER);
    jLabel2.setIcon(new javax.swing.ImageIcon(getClass().getResource("/loading.gif"))); // NOI18N

    javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
    getContentPane().setLayout(layout);
    layout.setHorizontalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(layout.createSequentialGroup()
            .addContainerGap()
            .addComponent(jLabel1)
            .addContainerGap(javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE))
        .addComponent(jLabel2, javax.swing.GroupLayout.Alignment.TRAILING, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
    );
    layout.setVerticalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(layout.createSequentialGroup()
            .addContainerGap()
            .addComponent(jLabel1)
            .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
            .addComponent(jLabel2)
            .addContainerGap())
    );

    pack();
}

Answer 1

Without knowing the full extent of what you are trying to do, it's not entirely possible to you an exact answer.

From the sounds of things your trying to run long running tasks within the context of the Event Dispatching Thread. This thread is responsible for, amongst other things, processing repaint requests.

Blocking this thread, prevents Swing from repainting itself.

From what I can tell, you want to use a SwingWorker. This will allow you to performing your work in a background thread, while re syncing updates back to the EDT

Updated with example

I know you said didn't "want" to use a SwingWorker, but to be honest, it's just simpler and safer...

import java.awt.BorderLayout;
import java.awt.EventQueue;
import java.awt.GridBagLayout;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.SwingWorker;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class LongRunningTask {

    public static void main(String[] args) {
        new LongRunningTask();
    }

    public LongRunningTask() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                }

                new BackgroundWorker().start();

            }
        });
    }

    public class BackgroundWorker extends SwingWorker<Object, Object> {

        private JFrame frame;

        public BackgroundWorker() {
        }

        // Cause exeute is final :P
        public void start() {
            ImageIcon icon = new ImageIcon(getClass().getResource("/spinner.gif"));
            JLabel label = new JLabel("This might take some time");
            label.setIcon(icon);

            frame = new JFrame("Testing");
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            frame.setLayout(new GridBagLayout());
            frame.add(label);
            frame.pack();
            frame.setLocationRelativeTo(null);
            frame.setVisible(true);

            execute();
        }

        @Override
        protected Object doInBackground() throws Exception {

            System.out.println("Working hard...");
            Thread.sleep(1000 + (((int)Math.round(Math.random() * 5)) * 1000));
            System.out.println("Or hardly working...");

            return null;

        }

        @Override
        protected void done() {
            frame.dispose();
        }

    }
}