Help me understand painting methods

[marcelo]

First of all, sorry if this is a dumb question. I'm quite new to Swing and I really appreciate some light on my issue.

I use NetBeans as my programming IDE and came up with a simple JFrame window example. I have a JPanel in which I want to modify its location from the constructor method. Let me show my code:

package myexample;

import java.awt.Point;

public class Example extends javax.swing.JFrame {

    public Example() {
        initComponents();
        pnlTitle.setLocation(new Point((int) pnlTitle.getLocation().getX(), (int) pnlTitle.getLocation().getY() + 100));
    }

    @SuppressWarnings("unchecked")
    private void initComponents() {

        pnlTitle = new javax.swing.JPanel();
        lblText = new javax.swing.JLabel();
        btnTest = new javax.swing.JButton();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

        lblText.setText("My label");

        javax.swing.GroupLayout pnlTitleLayout = new javax.swing.GroupLayout(pnlTitle);
        pnlTitle.setLayout(pnlTitleLayout);
        pnlTitleLayout.setHorizontalGroup(
            pnlTitleLayout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(pnlTitleLayout.createSequentialGroup()
                .addContainerGap()
                .addComponent(lblText)
                .addContainerGap(331, Short.MAX_VALUE))
        );
        pnlTitleLayout.setVerticalGroup(
            pnlTitleLayout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(pnlTitleLayout.createSequentialGroup()
                .addContainerGap()
                .addComponent(lblText)
                .addContainerGap(javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE))
        );

        btnTest.setText("Test");
        btnTest.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                btnTestActionPerformed(evt);
            }
        });

        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()
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                    .addComponent(pnlTitle, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                    .addComponent(btnTest, javax.swing.GroupLayout.Alignment.TRAILING))
                .addContainerGap())
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addContainerGap()
                .addComponent(pnlTitle, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, 219, Short.MAX_VALUE)
                .addComponent(btnTest)
                .addContainerGap())
        );

        pack();
    }                  

    private void btnTestActionPerformed(java.awt.event.ActionEvent evt) {                                        
        pnlTitle.setLocation(new Point((int) pnlTitle.getLocation().getX(), (int) pnlTitle.getLocation().getY() + 100));
    }                                       

    public static void main(String args[]) {

        try {
            for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
                if ("Nimbus".equals(info.getName())) {
                    javax.swing.UIManager.setLookAndFeel(info.getClassName());
                    break;
                }
            }
        } catch (ClassNotFoundException ex) {
            java.util.logging.Logger.getLogger(Example.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (InstantiationException ex) {
            java.util.logging.Logger.getLogger(Example.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            java.util.logging.Logger.getLogger(Example.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (javax.swing.UnsupportedLookAndFeelException ex) {
            java.util.logging.Logger.getLogger(Example.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        }

        java.awt.EventQueue.invokeLater(new Runnable() {

            public void run() {
                new Example().setVisible(true);
            }
        });
    }
                        
    private javax.swing.JButton btnTest;
    private javax.swing.JLabel lblText;
    private javax.swing.JPanel pnlTitle;
    // End of variables declaration                   
}

Unfortunately, the panel is in the old position, as defined by NetBeans generated method initComponents:



If I click in the button, the panel is correctly put in the place I want.

I'm pretty sure it's something related to a painting method, but I really can't figure out what it is. In this particular code, I really need to set the JPanel position again after its default position from the initComponents method. But I could not figure out which method I should invoke. I tried repaint, revalidate and a thousand more, but no luck. Besides, I'd like to understand what's happening.

I appreciate any help. Thanks!

[DarrylBurke]

I want to modify its location from the constructor method.

A constructor is not a method.

I'd like to understand what's happening.

Then drop the visual designer and learn to code the GUI yourself.
Trail: Creating a GUI With JFC/Swing (The Java™ Tutorials)
Omit the second subtopic listed. It'll only hamper the learning process.

db