Dynamic add component to panel, it does't work

Question

I want to add a label in a panel when you click button.
I used revalidate() and revalidate() method, but it didn't appear in panel.
HELP ME?? WHAT'S WRONG!
private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                        
jPanel1.add(new JLabel("Hello"));
jPanel1.revalidate();
jPanel1.repaint();
}

Answer 1

i add Layout manager to panel. It works. Thanks,
So tricky things for dynamic adding component:
1, setup layout manager to container (such as panel),
2, add component to container
3, call revalidate() method to relayout these components in container
You can't miss any one of those.
private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                        
jPanel1.setLayout(new FlowLayout());
jPanel1.add(new JButton("Hello"));
jPanel1.revalidate();
}