Container's validate does not update removal

Question

the validate() method does not update the display to show the remval of a component from a container. A way to go around: use repaint() instead.
Please see the following code:
import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTextField;
import javax.swing.JToolBar;
import net.effortech.harry.swing.Laf;
public class ScrollPaneViewPort extends JFrame {
  private JButton add = new JButton("Add");
  private JButton remove = new JButton("Remove");
  private JTextField field;
  private JScrollPane scrollPane;
  private ActionListener al = new ActionListener() {
    public void actionPerformed(ActionEvent e) {
      JButton s = (JButton) e.getSource();
      if (s == add) {
        add.setEnabled(false);
        remove.setEnabled(true);
        field = new JTextField();
        scrollPane = new JScrollPane(field,
            JScrollPane.VERTICAL_SCROLLBAR_NEVER,
            JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS);
        getContentPane().add(scrollPane, BorderLayout.SOUTH);
        validate();
      } else {
        add.setEnabled(true);
        remove.setEnabled(false);
        getContentPane().remove(scrollPane);
        validate();
        //repaint();
  public ScrollPaneViewPort() {
    super("ScrollPane ViewPort");
    JToolBar tb = new JToolBar();
    tb.add(add);
    remove.setEnabled(false);
    tb.add(remove);
    add.addActionListener(al);
    remove.addActionListener(al);
    getContentPane().add(tb, BorderLayout.NORTH);
    setBounds(100, 100, 500, 400);
    setDefaultCloseOperation(EXIT_ON_CLOSE);
    setVisible(true);
  public static void main(String[] args) {
    new ScrollPaneViewPort();
}

Answer 1

use repaint() insteadThat matches our experiences.