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    <p>By the time I wrote and tested the code below, you probably got lot of better answers...<br> I don't mind as I enjoyed the experiment/learning (still a bit green on the Swing front).</p> <p>[EDIT] Three years later, I am a bit less green, and I took in account the valid remarks of bobndrew. I have no problem with the key navigation that just works (perhaps it was a JVM version issue?). I improved the renderer to show highlight, though. And I use a better demo code. The accepted answer is probably better (more standard), mine is probably more flexible if you want a custom separator...</p> <p>The base idea is to use a renderer for the items of the combo box. For most items, it is a simple JLabel with the text of the item. For the last recent/most used item, I decorate the JLabel with a custom border drawing a line on its bottom.</p> <pre><code>import java.awt.*; import javax.swing.*; @SuppressWarnings("serial") public class TwoPartsComboBox extends JComboBox { private int m_lastFirstPartIndex; public TwoPartsComboBox(String[] itemsFirstPart, String[] itemsSecondPart) { super(itemsFirstPart); m_lastFirstPartIndex = itemsFirstPart.length - 1; for (int i = 0; i &lt; itemsSecondPart.length; i++) { insertItemAt(itemsSecondPart[i], i); } setRenderer(new JLRenderer()); } protected class JLRenderer extends JLabel implements ListCellRenderer { private JLabel m_lastFirstPart; public JLRenderer() { m_lastFirstPart = new JLabel(); m_lastFirstPart.setBorder(new BottomLineBorder()); // m_lastFirstPart.setBorder(new BottomLineBorder(10, Color.BLUE)); } @Override public Component getListCellRendererComponent( JList list, Object value, int index, boolean isSelected, boolean cellHasFocus) { if (value == null) { value = "Select an option"; } JLabel label = this; if (index == m_lastFirstPartIndex) { label = m_lastFirstPart; } label.setText(value.toString()); label.setBackground(isSelected ? list.getSelectionBackground() : list.getBackground()); label.setForeground(isSelected ? list.getSelectionForeground() : list.getForeground()); label.setOpaque(true); return label; } } } </code></pre> <p>Separator class, can be thick, with custom color, etc.</p> <pre><code>import java.awt.*; import javax.swing.border.AbstractBorder; /** * Draws a line at the bottom only. * Useful for making a separator in combo box, for example. */ @SuppressWarnings("serial") class BottomLineBorder extends AbstractBorder { private int m_thickness; private Color m_color; BottomLineBorder() { this(1, Color.BLACK); } BottomLineBorder(Color color) { this(1, color); } BottomLineBorder(int thickness, Color color) { m_thickness = thickness; m_color = color; } @Override public void paintBorder(Component c, Graphics g, int x, int y, int width, int height) { Graphics copy = g.create(); if (copy != null) { try { copy.translate(x, y); copy.setColor(m_color); copy.fillRect(0, height - m_thickness, width - 1, height - 1); } finally { copy.dispose(); } } } @Override public boolean isBorderOpaque() { return true; } @Override public Insets getBorderInsets(Component c) { return new Insets(0, 0, m_thickness, 0); } @Override public Insets getBorderInsets(Component c, Insets i) { i.left = i.top = i.right = 0; i.bottom = m_thickness; return i; } } </code></pre> <p>Test class:</p> <pre><code>import java.awt.*; import java.awt.event.*; import javax.swing.*; @SuppressWarnings("serial") public class TwoPartsComboBoxDemo extends JFrame { private TwoPartsComboBox m_combo; public TwoPartsComboBoxDemo() { Container cont = getContentPane(); cont.setLayout(new FlowLayout()); cont.add(new JLabel("Data: ")) ; String[] itemsRecent = new String[] { "ichi", "ni", "san" }; String[] itemsOther = new String[] { "one", "two", "three" }; m_combo = new TwoPartsComboBox(itemsRecent, itemsOther); m_combo.setSelectedIndex(-1); cont.add(m_combo); m_combo.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent ae) { String si = (String) m_combo.getSelectedItem(); System.out.println(si == null ? "No item selected" : si.toString()); } }); // Reference, to check we have similar behavior to standard combo JComboBox combo = new JComboBox(itemsRecent); cont.add(combo); } /** * Start the demo. * * @param args the command line arguments */ public static void main(String[] args) { // turn bold fonts off in metal UIManager.put("swing.boldMetal", Boolean.FALSE); SwingUtilities.invokeLater(new Runnable() { public void run() { JFrame demoFrame = new TwoPartsComboBoxDemo(); demoFrame.setTitle("Test GUI"); demoFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); demoFrame.setSize(400, 100); demoFrame.setVisible(true); } }); } } </code></pre>
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    1. POHow do I add a separator to a JComboBox in Java?
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    1. COYour variable-naming is not the worst thing here: You're breaking the whole combobox-item-selection: the selection is not painted anymore and the first-letter-key-jumps are broken. And you should define `m_combo` and `m_renderer` in the smallest possible scope (in `public TestGui()`). And should not use a glooooobal `m_lastRecentIndex` for the Renderer **and** the 'TestGui' class (which should be a lonely Main class, not a 'JFrame' subclass). But I like the braces-style!
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    2. CO@bobndrew: hey! As I wrote, I was a newbie at the time (3 years already!). Among sins you don't point out, I probably used some Swing test template I found and even worse, I didn't use SwingUtilities.invokeLater! The code I have currently uses it, at least (but it is still a JFrame subclass...). And m_lastRecentIndex is more local... But most of your criticism is about a quickly made test class, which isn't really production code. Today, I pay more attention to such code, as newbies can take inspiration from it... :-) Also, you are right about highlighting hovered elements and selection. TODO
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    3. CONote: I edited the code above for a more modern / correct version. One advantage of my approach is that it is more flexible (in look at least) than JSeparator and it doesn't take a slot.
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