Creation of components in dinamic way. Problem with threads....?

Question

hi,
I am trying to add components (JTextFields) to a JPanel in dynamic way.
I would like that the user decides the number of the components, to
be created, for executing a function by clicking a button.
But clicking on the button, the elaboration doesn't produce the creation
of the JTextFields.
Debugging the code I saw that the same function works well
when it is called from the normal data flow of the elaboration
instead that it is called from inside a listener.
It is hard for me to understand the reason why this
happens, as well I could think that this problem could happen
because the execution of different threads.
But I am not able to manage those kind of situations....
I would like to have a little help
thank you
regards
tonyMrsangelo.
To reproduce the problem I post some code where the function (setComponentInThePanel())
is called from the constructor of the class and from the listener of a JButton.
package labels;
import java.awt.Dimension;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JSpinner;
import javax.swing.JTextField;
import javax.swing.SpinnerNumberModel;
public class LabelsDialogMain extends JFrame {
    PanelCanvas jPanCanvas = new PanelCanvas();
    PanelDesign jPanDesign = new PanelDesign();
    PanelCommands jPanCommands = new PanelCommands(jPanDesign);
    /** Creates new form MainLabelsDialog */
    public LabelsDialogMain() {
        java.awt.GridBagConstraints gridBagConstraints;
        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        getContentPane().setLayout(new java.awt.GridBagLayout());
        gridBagConstraints = new java.awt.GridBagConstraints();
        gridBagConstraints.gridx = 0;
        gridBagConstraints.gridy = 0;
        gridBagConstraints.gridwidth = 2;
        gridBagConstraints.gridheight = 2;
        getContentPane().add(jPanCanvas, gridBagConstraints);
        gridBagConstraints = new java.awt.GridBagConstraints();
        gridBagConstraints.gridx = 3;
        gridBagConstraints.gridy = 0;
        gridBagConstraints.gridwidth = 2;
        gridBagConstraints.gridheight = 2;
        getContentPane().add(jPanDesign, gridBagConstraints);
        gridBagConstraints = new java.awt.GridBagConstraints();
        gridBagConstraints.gridx = 1;
        gridBagConstraints.gridy = 2;
        gridBagConstraints.gridwidth = 4;
        gridBagConstraints.gridheight = 2;
        getContentPane().add(jPanCommands, gridBagConstraints);
        pack();
     * @param args the command line arguments
    public static void main(String args[]) {
         LabelsDialogMain mld = new LabelsDialogMain();
         mld.setVisible(true);
class PanelCanvas extends JPanel {
    public PanelCanvas() {
        Dimension d = new Dimension(400,200);
        setPreferredSize(d);
        setBorder(javax.swing.BorderFactory.createTitledBorder(null, "Panel Canvas", javax.swing.border.TitledBorder.DEFAULT_JUSTIFICATION, javax.swing.border.TitledBorder.DEFAULT_POSITION, new java.awt.Font("Comic Sans MS", 0, 11), new java.awt.Color(0, 255, 255))); // NOI18N
} // class PanelCanvas
class PanelDesign extends JPanel {
    JTextField textField [];
    public PanelDesign() {
        Dimension d = new Dimension(400,200);
        setPreferredSize(d);
        setBorder(javax.swing.BorderFactory.createTitledBorder(null, "Panel Design", javax.swing.border.TitledBorder.DEFAULT_JUSTIFICATION, javax.swing.border.TitledBorder.DEFAULT_POSITION, new java.awt.Font("Comic Sans MS", 0, 11), new java.awt.Color(0, 255, 255))); // NOI18N
    void setComponentInThePanel(int dim ){
         textField = new  JTextField[dim];
         for (int i = 0; i < dim; i++){
             textField[i] = new  JTextField("----- " + i);
             add(textField);
System.out.println("executed the nmbr: " + i);
repaint();
} // setComponentInThePanel()
} // class PanelDesign
class PanelCommands extends JPanel {
PanelDesign panelDesign;
private javax.swing.JLabel jLblRowNmbr;
private javax.swing.JSpinner jSpinner;
JButton dummyButton = new JButton("button");
public PanelCommands(PanelDesign pnlDesign) {
panelDesign = pnlDesign;
Dimension d = new Dimension(800,200);
setPreferredSize(d);
setBorder(javax.swing.BorderFactory.createTitledBorder(null, "Panel Cmmands", javax.swing.border.TitledBorder.DEFAULT_JUSTIFICATION, javax.swing.border.TitledBorder.DEFAULT_POSITION, new java.awt.Font("Comic Sans MS", 0, 11), new java.awt.Color(0, 255, 255))); // NOI18N
jLblRowNmbr = new javax.swing.JLabel();
jSpinner = new JSpinner();
jLblRowNmbr = new JLabel();
add(jLblRowNmbr);
add(jSpinner);
add(dummyButton);
jSpinner.setModel(new javax.swing.SpinnerNumberModel(Short.valueOf((short)1), Short.valueOf((short)1), null, Short.valueOf((short)1)));
final SpinnerNumberModel sm = (SpinnerNumberModel) this.jSpinner.getModel();
jLblRowNmbr.setText("N. of the rows");
// panelDesign.setComponentInThePanel(4); "take out the comment of this row to get the creation of JTextFields"
dummyButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
Number amp = sm.getNumber();
int ampInt = amp.intValue();
panelDesign.setComponentInThePanel(ampInt);
// panelDesign.setComponentInThePanel(4);
JOptionPane.showMessageDialog(jSpinner, "spinner = " + ampInt);
} // class PanelCommands

Answer 1

When you add/remove components to a panel when the GUI has already been created then you need to use:
panel.revalidate();
panel.repaint();