JTable goes blank for second time when JButton is pressed

Question

I am trying to load file name along with few details in the JTable, first time when I press the button, it loads fine , but for the second time when I press the same button it goes blank .

Short example:

package exampleDemo;

public class JTableExample {

private JFrame frame;
private JTable table_1;

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

public JTableExample() {
    initialize();
}

    public void showEmptyTable() {
        final String[] colNames = {"Sl.no.", "File Name", "Size", "Last Modified", "PO", "LN", "SI", "MS", "PT"};
        final String[][] emptyData = {
            {"", "", "", "", "", "", "", "", "",},
            {"", "", "", "", "", "", "", "", "", },
            {"", "", "", "", "", "", "", "", "", },
            {"", "", "", "", "", "", "", "", "", },
            {"", "", "", "", "", "", "", "", "", },};
    table_1.setModel(new DefaultTableModel(emptyData, colNames));
    frame.getContentPane().add(table_1);
    JScrollPane scrollPane = new JScrollPane(table_1);
    scrollPane.setBounds(81, 162, 830, 180);
    frame.getContentPane().add(scrollPane);
};

private void initialize() {
    frame = new JFrame();
    frame.setBounds(100, 100, 1002, 576);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.getContentPane().setLayout(null);

    table_1 = new JTable();
    table_1.setBounds(81, 162, 830, 180);
    frame.getContentPane().add(table_1);

    JButton btnNewButton = new JButton("New button");
    btnNewButton.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent arg0) {
            table_1.repaint(); 
            showEmptyTable();
        }
    });
    btnNewButton.setBounds(578, 70, 89, 23);
    frame.getContentPane().add(btnNewButton);
    }
}

Answer 1

A quick glance at your code would suggest to me that you're going about this the wrong way: you're literally reconstructing a new table model each time you click the button and I suspect (although it's just a hunch at the moment) is because each time you click that button you're adding the same table via a new scrollpanel to the main JFrame - each and every time.

What you want to do is initialise the table and its model during the loading of the frame. And then if you want to clear the table, then simply get the reference to that table's model and manipulate the existing model. That's it - no need to create an entire new model; no need to add a new table via a scrollpanel.

So what I'd do in your case is add a line to your constructor:

public YourClassName() {
  initialize();
  initializeYourTable();
}

Then initializeYourTable() would look like this:

private void initSearchTable() {
    final String[] colNames = {"Sl.no.", "File Name", "Size", "Last Modified", "PO", "LN", "SI", "MS", "PT"};
    //PO: Part Order
    //LN: Line Number
    //SI: Serial Number
    //MS: Material Supplier
    //PT: Part Item 
    final String[][] emptyData = {
        {"", "", "", "", "", "", "", "", "",},
        {"", "", "", "", "", "", "", "", "",},
        {"", "", "", "", "", "", "", "", "",},
        {"", "", "", "", "", "", "", "", "",},
        {"", "", "", "", "", "", "", "", "",},};
    table_3.setModel(new DefaultTableModel(emptyData, colNames));
    //frmViperManufacturingRecord.getContentPane().add(table_3); <-- NB this should be commented out!!
    table_3.setAutoResizeMode(JTable.AUTO_RESIZE_OFF);
    table_3.getColumnModel().getColumn(0).setPreferredWidth(40);
    table_3.getColumnModel().getColumn(1).setPreferredWidth(290);
    table_3.getColumnModel().getColumn(2).setPreferredWidth(80);
    table_3.getColumnModel().getColumn(3).setPreferredWidth(178);
    table_3.getColumnModel().getColumn(4).setPreferredWidth(25);
    table_3.getColumnModel().getColumn(5).setPreferredWidth(25);
    table_3.getColumnModel().getColumn(6).setPreferredWidth(25);
    table_3.getColumnModel().getColumn(7).setPreferredWidth(25);
    table_3.getColumnModel().getColumn(8).setPreferredWidth(25);
    JScrollPane scrollPane = new JScrollPane(table_3);
    scrollPane.setBounds(324, 209, 713, 160);
    frmViperManufacturingRecord.getContentPane().add(scrollPane);
}

To clear the table you can use this shortcut :

private void resetTable() {
    DefaultTableModel model = (DefaultTableModel)table_3.getModel();
    model.setRowCount(0);
}

And therefore you need to change your actionPerformed :

public void actionPerformed(ActionEvent arg0) {
  table_3.repaint();
  //showEmptyTable();
  resetTable();
}