How do I make a JOptionPane dropdown that has a preset option that is not choosable?

Say I am making a program that keeps track of people's favorite food. I have a dropdown, as such:

String foods = { "Pizza", "Burgers", "Pasta", "Bacon" };
String favoriteFood = JOptionPane.showInputDialog(null, "What is your favorite food?", "Choice", JOptionPane.QUESTION_MESSAGE, null, foods, foods[0]));
JOptionPane.showMessageDialog(null, favoriteFood);

How do I make a part in the dropdown that is like "Choose now...", but if you click the "Choose now...", it doesn't become your choice? Thank you!

Solution

You may do it like this

String[] foods = { "Pizza", "Burgers", "Pasta", "Bacon" };
JComboBox<String> cb = new JComboBox<String>(foods);
cb.getModel().setSelectedItem("Choose now...");

cb.addHierarchyListener(hEv -> {
    if((hEv.getChangeFlags() & HierarchyEvent.SHOWING_CHANGED) != 0 && cb.isShowing()) {
        JButton ok = SwingUtilities.getRootPane(cb).getDefaultButton();
        ok.setEnabled(cb.getSelectedIndex() >= 0);
        cb.addActionListener(aEv -> ok.setEnabled(cb.getSelectedIndex() >= 0));
}   });

JPanel p = new JPanel(new GridLayout(0, 1, 0, 8));
p.add(new JLabel("What is your favorite food?"));
p.add(cb);

int choice = JOptionPane.showConfirmDialog(null,
    p, "Choice", JOptionPane.OK_CANCEL_OPTION, JOptionPane.QUESTION_MESSAGE);

JOptionPane.showMessageDialog(null,
    choice == JOptionPane.OK_OPTION? cb.getSelectedItem(): "no choice");

The first challenge is to set a (pre)selected value that is not part of the selectable choices. When you call setSelectedItem on a non-editable JComboBox, it will reject any values outside the model. However, we can set the selected value on the model directly, like in cb.getModel().setSelectedItem("Choose now...");

Then, to ensure that we won’t confuse this initial selection with an actual selection, we have to disable the “Ok” button until a choice from the list has been made (cb.getSelectedIndex() >= 0). To get the “Ok” button itself, we wait until the entire AWT hierarchy has been constructed and get the default button.