CardLayoutを設定したパネル上にOverlayLayoutでカード切り替え用のJComboBoxを配置する

String[] model = {"red", "green", "blue"};

CardLayout cardLayout = new CardLayout();
JPanel cards = new JPanel(cardLayout);
cards.add(makePanel(Color.RED), model[0]);
cards.add(makePanel(Color.GREEN), model[1]);
cards.add(makePanel(Color.BLUE), model[2]);

JComboBox<String> combo = new JComboBox<>(model);
combo.addItemListener(e -> {
  if (e.getStateChange() == ItemEvent.SELECTED) {
    cardLayout.show(cards, Objects.toString(e.getItem()));
  }
});

JPanel pp = new JPanel(new BorderLayout());
pp.setOpaque(false);
pp.setBorder(BorderFactory.createEmptyBorder(8, 24, 0, 24));
pp.add(combo, BorderLayout.NORTH);

JPanel p = new JPanel() {
  @Override public boolean isOptimizedDrawingEnabled() {
    return false;
  }
};
p.setLayout(new OverlayLayout(p));
p.add(pp);
p.add(cards);