Why JComboBox ignore PrototypeDisplayValue

Question

In connections with these two post @iMohammad, Increasing/Decreasing Font Size inside textArea using JButton and Changing Font Style when Clicking on a JButton Java ..., I'm facing with really funny issue that came from JComboBoxby passing setPrototypeDisplayValue as an argument for JComboBox's size on the screen

please how can I resize JComboBox dynamically depends of Font, same as works correctly for another JComponents that I tried in my sscce

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class ComboBoxFontChange extends JFrame {

    private static final long serialVersionUID = 1L;
    private JComboBox cbox = new JComboBox();
    private JTextField tfield = new JTextField("Change");
    private JLabel label = new JLabel("Cash");
    private JButton button = new JButton("++ Font");
    private JTextField text;
    private JPanel panel = new JPanel();

    public ComboBoxFontChange() {
        super("Combo Box Font change");
        text = (JTextField) cbox.getEditor().getEditorComponent();
        cbox.addItem("Change");
        cbox.addItem("Cash");
        cbox.addItem("Font");
        tfield.setColumns(5);
        button.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent e) {
                Font font = cbox.getFont();
                font = font.deriveFont((float) (font.getSize2D() * 1.10));
                cbox.setFont(font);
                // EDIT
                cbox.setPrototypeDisplayValue(cbox.getSelectedItem().toString());
                tfield.setFont(font);
                button.setFont(font);
                label.setFont(font);
                //panel.revalidate();
                //panel.repaint();
                pack();
            }
        });
        //panel.setLayout(new GridLayout(2, 2, 10, 10));
        panel.add(cbox);
        panel.add(label);
        panel.add(tfield);
        panel.add(button);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        add(panel);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {

            @Override
            public void run() {
                ComboBoxFontChange frame = new ComboBoxFontChange();
                frame.pack();
                frame.setVisible(true);
            }
        });
    }
}

Answer 1

I debugged your SSCCE, and the value passed to setPrototypeDisplayValue is the empty string. Changing the line to

cbox.setPrototypeDisplayValue(cbox.getSelectedItem());

Makes everything work as expected. Removing the call to setPrototypDisplayValue also makes the program behave as expected.

EDIT:

The other problem is that no event is fired for the prototype display value because you set it to the previous value as before, and an event is only fired if the value actually changes. Adding cbox.setPrototypeDisplayValue(""); before cbox.setPrototypeDisplayValue(cbox.getSelectedItem().toString()) makes everything behave as expected, even on JDK 1.6. I agree that given that the font is changed, the preferred size should be recomputed, but at least this change is a workaround.