Java Tutorial/Swing/JComboBox

A Color Combo Box Editor

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.ruponent;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.ruboBoxEditor;
import javax.swing.JButton;
import javax.swing.JColorChooser;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.event.EventListenerList;
class ColorComboBoxEditor implements ComboBoxEditor {
  final protected JButton editor;
  protected EventListenerList listenerList = new EventListenerList();
  public ColorComboBoxEditor(Color initialColor) {
    editor = new JButton("");
    editor.setBackground(initialColor);
    ActionListener actionListener = new ActionListener() {
      public void actionPerformed(ActionEvent e) {
        Color currentBackground = editor.getBackground();
        Color color = JColorChooser.showDialog(editor, "Color Chooser", currentBackground);
        if ((color != null) && (currentBackground != color)) {
          editor.setBackground(color);
          fireActionEvent(color);
        }
      }
    };
    editor.addActionListener(actionListener);
  }
  public void addActionListener(ActionListener l) {
    listenerList.add(ActionListener.class, l);
  }
  public Component getEditorComponent() {
    return editor;
  }
  public Object getItem() {
    return editor.getBackground();
  }
  public void removeActionListener(ActionListener l) {
    listenerList.remove(ActionListener.class, l);
  }
  public void selectAll() {
    // Ignore
  }
  public void setItem(Object newValue) {
    if (newValue instanceof Color) {
      Color color = (Color) newValue;
      editor.setBackground(color);
    } else {
      try {
        Color color = Color.decode(newValue.toString());
        editor.setBackground(color);
      } catch (NumberFormatException e) {
      }
    }
  }
  protected void fireActionEvent(Color color) {
    Object listeners[] = listenerList.getListenerList();
    for (int i = listeners.length - 2; i >= 0; i -= 2) {
      if (listeners[i] == ActionListener.class) {
        ActionEvent actionEvent = new ActionEvent(editor, ActionEvent.ACTION_PERFORMED, color
            .toString());
        ((ActionListener) listeners[i + 1]).actionPerformed(actionEvent);
      }
    }
  }
}
public class ColorComboBoxEditorDemo {
  public static void main(String args[]) {
    Color colors[] = { Color.RED, Color.BLUE, Color.BLACK, Color.WHITE };
    JFrame frame = new JFrame("Editable JComboBox");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    final JComboBox comboBox = new JComboBox(colors);
    comboBox.setEditable(true);
    comboBox.setEditor(new ColorComboBoxEditor(Color.RED));
    frame.add(comboBox, BorderLayout.NORTH);
    frame.setSize(300, 200);
    frame.setVisible(true);
  }
}

Add an item after the first item

import javax.swing.JComboBox;
public class Main {
  public static void main(String[] argv) throws Exception {
    String[] items = { "item1", "item2" };
    JComboBox cb = new JComboBox(items);
    cb.insertItemAt("item0.5", 1);
  }
}

Add an item to the end of the list

import javax.swing.JComboBox;
public class Main {
  public static void main(String[] argv) throws Exception {
    String[] items = { "item1", "item2" };
    JComboBox cb = new JComboBox(items);
    cb.addItem("item3");
  }
}

Adding and Removing an Item in a JComboBox Component

import javax.swing.JComboBox;
public class Main {
  public static void main(String[] argv) throws Exception {
    String[] items = { "item1", "item2" };
    JComboBox cb = new JComboBox(items);
    // Add an item to the start of the list
    cb.insertItemAt("item0", 0);
  }
}

Add Items to JComboBox

import javax.swing.JComboBox;
import javax.swing.JFrame;
public class AddingItemToComboBox {
  public static void main(String[] a) {
    JFrame frame = new JFrame();
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    JComboBox jComboBox1 = new JComboBox();
    jComboBox1.addItem("asdf");
    Object cmboitem = jComboBox1.getSelectedItem();
    System.out.println(cmboitem);
    frame.add(jComboBox1);
    frame.setSize(300, 200);
    frame.setVisible(true);
  }
}

Combobox cell renderer

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.ruponent;
import java.awt.Font;
import java.awt.Graphics;
import javax.swing.DefaultListCellRenderer;
import javax.swing.Icon;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JList;
import javax.swing.ListCellRenderer;
class ComplexCellRenderer implements ListCellRenderer {
  protected DefaultListCellRenderer defaultRenderer = new DefaultListCellRenderer();
  public Component getListCellRendererComponent(JList list, Object value, int index,
      boolean isSelected, boolean cellHasFocus) {
    Font theFont = null;
    Color theForeground = null;
    Icon theIcon = null;
    String theText = null;
    JLabel renderer = (JLabel) defaultRenderer.getListCellRendererComponent(list, value, index,
        isSelected, cellHasFocus);
    if (value instanceof Object[]) {
      Object values[] = (Object[]) value;
      theFont = (Font) values[0];
      theForeground = (Color) values[1];
      theIcon = (Icon) values[2];
      theText = (String) values[3];
    } else {
      theFont = list.getFont();
      theForeground = list.getForeground();
      theText = "";
    }
    if (!isSelected) {
      renderer.setForeground(theForeground);
    }
    if (theIcon != null) {
      renderer.setIcon(theIcon);
    }
    renderer.setText(theText);
    renderer.setFont(theFont);
    return renderer;
  }
}
public class ComplexRenderingSample {
  public static void main(String args[]) {
    Object elements[][] = {
        { new Font("Helvetica", Font.PLAIN, 20), Color.RED, new MyIcon(), "A" },
        { new Font("TimesRoman", Font.BOLD, 14), Color.BLUE, new MyIcon(), "A" },
        { new Font("Courier", Font.ITALIC, 18), Color.GREEN, new MyIcon(), "A" },
        { new Font("Helvetica", Font.BOLD | Font.ITALIC, 12), Color.GRAY, new MyIcon(), "A" },
        { new Font("TimesRoman", Font.PLAIN, 32), Color.PINK, new MyIcon(), "A" },
        { new Font("Courier", Font.BOLD, 16), Color.YELLOW, new MyIcon(), "A" },
        { new Font("Helvetica", Font.ITALIC, 8), Color.DARK_GRAY, new MyIcon(), "A" } };
    JFrame frame = new JFrame("Complex Renderer");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    ListCellRenderer renderer = new ComplexCellRenderer();
    JComboBox comboBox = new JComboBox(elements);
    comboBox.setRenderer(renderer);
    frame.add(comboBox, BorderLayout.NORTH);
    
    frame.setSize(300, 200);
    frame.setVisible(true);
  }
}
class MyIcon implements Icon {
  public MyIcon() {
  }
  public int getIconHeight() {
    return 20;
  }
  public int getIconWidth() {
    return 20;
  }
  public void paintIcon(Component c, Graphics g, int x, int y) {
    g.setColor(Color.RED);
    g.drawRect(0, 0, 25, 25);
  }
}

Creating JComboBox Components

public JComboBox()
JComboBox comboBox = new JComboBox();
public JComboBox(Object listData[])
String labels[] = { "A", "B", "C", "D", "E"};
JComboBox comboBox = new JComboBox(labels);
public JComboBox(Vector listData)
Vector vector = aBufferedImage.getSources();
JComboBox comboBox = new JComboBox(vector);
public JComboBox(ComboBoxModel model)
ResultSet results = aJDBCStatement.executeQuery("SELECT columnName FROM tableName");
DefaultComboBoxModel model = new DefaultComboBoxModel();
while (result.next())
  model.addElement(results.getString(1));
JComboBox comboBox = new JComboBox(model);

Customizing a JComboBox Look and Feel

Property StringObject TypeComboBox.actionMapActionMapComboBox.ancestorInputMapInputMapComboBox.backgroundColorComboBox.borderBorderComboBox.buttonBackgroundColorComboBox.buttonDarkShadowColorComboBox.buttonHighlightColorComboBox.buttonShadowColorComboBox.controlColorComboBox.controlForegroundColorComboBox.disabledBackgroundColorComboBox.disabledForegroundColorComboBox.fontFontComboBox.foregroundColorComboBox.rendererUseListColorsBooleanComboBox.selectionBackgroundColorComboBox.selectionForegroundColorComboBox.showPopupOnNavigationBooleanComboBox.timeFactorLongComboBox.togglePopupTextStringComboBoxUIString

Custom JComboBox Pop-up Button

import java.awt.BorderLayout;
import javax.swing.JButton;
import javax.swing.JComboBox;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.plaf.ruboBoxUI;
import javax.swing.plaf.ruponentUI;
import javax.swing.plaf.basic.BasicArrowButton;
import javax.swing.plaf.basic.BasicComboBoxUI;
public class PopupComboSample {
  public static void main(String args[]) {
    String labels[] = { "A", "B", "C", "D", "E", "F", "G" };
    JFrame frame = new JFrame("Popup JComboBox");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    JComboBox comboBox = new JComboBox(labels);
    comboBox.setUI((ComboBoxUI) MyComboBoxUI.createUI(comboBox));
    frame.add(comboBox, BorderLayout.NORTH);
    frame.setSize(300, 200);
    frame.setVisible(true);
  }
  static class MyComboBoxUI extends BasicComboBoxUI {
    public static ComponentUI createUI(JComponent c) {
      return new MyComboBoxUI();
    }
    protected JButton createArrowButton() {
      JButton button = new BasicArrowButton(BasicArrowButton.EAST);
      return button;
    }
  }
}

Determining If the Menu of a JComboBox Component Is Visible

import javax.swing.JComboBox;
public class Main {
  public static void main(String[] argv) throws Exception {
    String[] items = { "item1", "item2" };
    JComboBox cb = new JComboBox(items);
    // Determine if the menu is visible
    boolean isVisible = cb.isPopupVisible();
  }
}

Determining When the Menu of a JComboBox Component Is Displayed

import javax.swing.JComboBox;
import javax.swing.event.PopupMenuEvent;
import javax.swing.event.PopupMenuListener;
public class Main {
  public static void main(String[] argv) throws Exception {
    String[] items = { "item1", "item2" };
    JComboBox cb = new JComboBox(items);
    cb.setEditable(true);
    MyPopupMenuListener actionListener = new MyPopupMenuListener();
    cb.addPopupMenuListener(actionListener);
  }
}
class MyPopupMenuListener implements PopupMenuListener {
  public void popupMenuWillBecomeVisible(PopupMenuEvent evt) {
    JComboBox cb = (JComboBox) evt.getSource();
  }
  public void popupMenuWillBecomeInvisible(PopupMenuEvent evt) {
    JComboBox cb = (JComboBox) evt.getSource();
  }
  public void popupMenuCanceled(PopupMenuEvent evt) {
    JComboBox cb = (JComboBox) evt.getSource();
  }
}

Displaying the Menu in a JComboBox Component Using a Keystroke

import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import javax.swing.JComboBox;
public class Main {
  public static void main(String[] argv) throws Exception {
    String[] items = { "A", "A", "B", "B", "C", "C" };
    JComboBox cb = new JComboBox(items);
    // Create and register the key listener
    cb.addKeyListener(new MyKeyListener());
  }
}
class MyKeyListener extends KeyAdapter {
  public void keyPressed(KeyEvent evt) {
    JComboBox cb = (JComboBox) evt.getSource();
    // Get pressed character
    char ch = evt.getKeyChar();
    // If not a printable character, return
    if (ch != KeyEvent.CHAR_UNDEFINED) {
      cb.showPopup();
    }
  }
}

Displaying the Menu in a JComboBox Component Using a Keystroke If the Selected Item Is Not Unique

import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import javax.swing.JComboBox;
public class Main {
  public static void main(String[] argv) throws Exception {
    String[] items = { "A", "A", "B", "B", "C" };
    JComboBox cb = new JComboBox(items);
    // Create and register the key listener
    cb.addKeyListener(new MyKeyListener());
  }
}
class MyKeyListener extends KeyAdapter {
  public void keyPressed(KeyEvent evt) {
    JComboBox cb = (JComboBox) evt.getSource();
    int curIx = cb.getSelectedIndex();
    char ch = evt.getKeyChar();
    JComboBox.KeySelectionManager ksm = cb.getKeySelectionManager();
    if (ksm != null) {
      // Determine if another item has the same prefix
      int ix = ksm.selectionForKey(ch, cb.getModel());
      boolean noMatch = ix < 0;
      boolean uniqueItem = ix == curIx;
      // Display menu if no matching items or the if the selection is not unique
      if (noMatch || !uniqueItem) {
        cb.showPopup();
      }
    }
  }
}

Editable JComboBox

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import javax.swing.JComboBox;
import javax.swing.JFrame;
public class Main extends JFrame {
  JComboBox combo = new JComboBox();
  public Main() {
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    combo.addItem("A");
    combo.addItem("H");
    combo.addItem("P");
    combo.setEditable(true);
    System.out.println("#items=" + combo.getItemCount());
    combo.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent e) {
        System.out.println("Selected index=" + combo.getSelectedIndex()
            + " Selected item=" + combo.getSelectedItem());
      }
    });
    getContentPane().add(combo);
    pack();
    setVisible(true);
  }
  public static void main(String arg[]) {
    new Main();
  }
}

Editing JComboBox Elements

import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JComboBox;
import javax.swing.JFrame;
public class EditComboBox {
  public static void main(String args[]) {
    String labels[] = { "A", "B", "C", "D", "E", "F", "G" };
    JFrame frame = new JFrame("Editable JComboBox");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    final JComboBox comboBox = new JComboBox(labels);
    comboBox.setMaximumRowCount(5);
    comboBox.setEditable(true);
    frame.add(comboBox, BorderLayout.NORTH);
    ActionListener actionListener = new ActionListener() {
      public void actionPerformed(ActionEvent actionEvent) {
        System.out.println("Selected: " + comboBox.getSelectedItem());
        System.out.println(", Position: " + comboBox.getSelectedIndex());
      }
    };
    comboBox.addActionListener(actionListener);
    frame.setSize(300, 200);
    frame.setVisible(true);
  }
}

Get Model from JComboBox and set it to JList

import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JList;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
public class Lister {
  public static void main(String[] args) {
    JFrame frame = new JFrame("Lister v1.0");
    String[] items = { "A", "B", "C" };
    JComboBox comboBox = new JComboBox(items);
    comboBox.setEditable(true);
    final JList list = new JList(comboBox.getModel());
    JButton button = new JButton("Per favore");
    button.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent ae) {
        Object[] selection = list.getSelectedValues();
        for (Object s : selection)
          System.out.println(s);
      }
    });
    JPanel comboPanel = new JPanel();
    comboPanel.add(comboBox);
    frame.add(comboPanel, BorderLayout.NORTH);
    frame.add(new JScrollPane(list), BorderLayout.CENTER);
    frame.add(button, BorderLayout.SOUTH);
    frame.setSize(200, 200);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setVisible(true);
  }
}

Get selected Item from JComboBox

import java.awt.event.ActionEvent;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JList;
public class GettingSettingSelectedItem {
  public static void main(String[] a) {
    JFrame frame = new JFrame();
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    JButton jButton1 = new JButton("Button");
    String[] mystring = { "Java", "JBuilder", "JFC", "Swing" };
    final JList jList1 = new JList(mystring);
    jButton1.addActionListener(new java.awt.event.ActionListener() {
      public void actionPerformed(ActionEvent e) {
        Object contents = jList1.getSelectedValue();
        System.out.println(contents);
      }
    });
    frame.add(jList1, "Center");
    frame.add(jButton1,"South");
    frame.setSize(300, 200);
    frame.setVisible(true);
  }
}

Getting and Setting the Selected Item in a JComboBox Component

import javax.swing.JComboBox;
public class Main {
  public static void main(String[] argv) throws Exception {
    String[] items = { "item1", "item2" };
    JComboBox cb = new JComboBox(items);
    // Get current value
    Object obj = cb.getSelectedItem(); 
    // Set a new value
    cb.setSelectedItem("item2");
    obj = cb.getSelectedItem(); 
    // If the new value is not in the list of valid items, the call is ignored
    cb.setSelectedItem("item3");
    obj = cb.getSelectedItem(); 
  }
}

Getting the Items in a JComboBox Component

import javax.swing.JComboBox;
public class Main {
  public static void main(String[] argv) throws Exception {
    String[] items = { "item1", "item2", "item3" };
    JComboBox cb = new JComboBox(items);
    // Get number of items
    int num = cb.getItemCount();
    // Get items
    for (int i = 0; i < num; i++) {
      Object item = cb.getItemAt(i);
    }
  }
}

If the combobox is editable, the new value can be any value

import javax.swing.JComboBox;
public class Main {
  public static void main(String[] argv) throws Exception {
    // Create a read-only combobox
    String[] items = { "item1", "item2" };
    JComboBox cb = new JComboBox(items);
    cb.setEditable(true);
    cb.setSelectedItem("item3");
    Object obj = cb.getSelectedItem(); 
  }
}

JComboBox Using the Custom Model

import javax.swing.AbstractListModel;
import javax.swing.ruboBoxModel;
import javax.swing.JComboBox;
import javax.swing.JFrame;
class MyComboBoxModel extends AbstractListModel implements ComboBoxModel {
  String[] ComputerComps = { "Monitor", "Key Board", "Mouse", "Joy Stick", "Modem", "CD ROM",
      "RAM Chip", "Diskette" };
  String selection = null;
  public Object getElementAt(int index) {
    return ComputerComps[index];
  }
  public int getSize() {
    return ComputerComps.length;
  }
  public void setSelectedItem(Object anItem) {
    selection = (String) anItem; // to select and register an
  } // item from the pull-down list
  // Methods implemented from the interface ComboBoxModel
  public Object getSelectedItem() {
    return selection; // to add the selection to the combo box
  }
}
public class JComboBoxModel {
  public static void main(String[] a){
    JFrame frame = new JFrame();
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    JComboBox cbox = new JComboBox(new MyComboBoxModel());  
    cbox.setMaximumRowCount(5);   
    frame.add(cbox);   
    
    frame.setSize(300, 200);
    frame.setVisible(true);
  }

}

Listening for Action Events from a JComboBox Component

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JComboBox;
public class Main {
  public static void main(String[] argv) throws Exception {
    String[] items = { "item1", "item2" };
    JComboBox cb = new JComboBox(items);
    cb.setEditable(true);
    // Create and register listener
    MyActionListener actionListener = new MyActionListener();
    cb.addActionListener(actionListener);
  }
}
class MyActionListener implements ActionListener {
  Object oldItem;
  public void actionPerformed(ActionEvent evt) {
    JComboBox cb = (JComboBox) evt.getSource();
    Object newItem = cb.getSelectedItem();
    boolean same = newItem.equals(oldItem);
    oldItem = newItem;
    if ("comboBoxEdited".equals(evt.getActionCommand())) {
      // User has typed in a string; only possible with an editable combobox
    } else if ("comboBoxChanged".equals(evt.getActionCommand())) {
      // User has selected an item; it may be the same item
    }
  }
}

Listening for Changes to the Selected Item in a JComboBox Component

import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;
import javax.swing.JComboBox;
public class Main {
  public static void main(String[] argv) throws Exception {
    String[] items = { "item1", "item2" };
    JComboBox cb = new JComboBox(items);
    cb.setEditable(true);
    MyItemListener actionListener = new MyItemListener();
    cb.addItemListener(actionListener);
  }
}
class MyItemListener implements ItemListener {
  // This method is called only if a new item has been selected.
  public void itemStateChanged(ItemEvent evt) {
    JComboBox cb = (JComboBox) evt.getSource();
    Object item = evt.getItem();
    if (evt.getStateChange() == ItemEvent.SELECTED) {
      // Item was just selected
    } else if (evt.getStateChange() == ItemEvent.DESELECTED) {
      // Item is no longer selected
    }
  }
}

Listening to Keyboard Events with a KeySelectionManager

import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JComboBox;
import javax.swing.JFrame;
public class SelectingComboSample {
  public static void main(String args[]) {
    String labels[] = { "A", "B", "C", "D", "E", "F" };
    JFrame frame = new JFrame("Selecting JComboBox");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    JComboBox comboBox = new JComboBox(labels);
    frame.add(comboBox, BorderLayout.SOUTH);
    JComboBox.KeySelectionManager manager =
      new JComboBox.KeySelectionManager() {
        public int selectionForKey(char aKey, ComboBoxModel aModel) {
          System.out.println(aKey);
          return -1;
        }
      };
    comboBox.setKeySelectionManager(manager);
    frame.setSize(400, 200);
    frame.setVisible(true);
  }
}

Listen to JComboBox with ItemListener

You can listen with an ActionListener or an ItemListener to find out when the selected item of the JComboBox changes.

import java.awt.BorderLayout;
import java.awt.ItemSelectable;
import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;
import javax.swing.JComboBox;
import javax.swing.JFrame;
public class ItemListenerSelectingComboSample {
  static private String selectedString(ItemSelectable is) {
    Object selected[] = is.getSelectedObjects();
    return ((selected.length == 0) ? "null" : (String) selected[0]);
  }
  public static void main(String args[]) {
    String labels[] = { "A", "B", "C", "D", "E", "F" };
    JFrame frame = new JFrame("Selecting JComboBox");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    JComboBox comboBox = new JComboBox(labels);
    frame.add(comboBox, BorderLayout.SOUTH);
    ItemListener itemListener = new ItemListener() {
      public void itemStateChanged(ItemEvent itemEvent) {
        int state = itemEvent.getStateChange();
        System.out.println((state == ItemEvent.SELECTED) ? "Selected" : "Deselected");
        System.out.println("Item: " + itemEvent.getItem());
        ItemSelectable is = itemEvent.getItemSelectable();
        System.out.println(", Selected: " + selectedString(is));
      }
    };
    comboBox.addItemListener(itemListener);
    frame.setSize(400, 200);
    frame.setVisible(true);
  }
}

Remove all items

import javax.swing.JComboBox;
public class Main {
  public static void main(String[] argv) throws Exception {
    String[] items = { "item1", "item2" };
    JComboBox cb = new JComboBox(items);
    cb.removeAllItems();
  }
}

Remove first item

import javax.swing.JComboBox;
public class Main {
  public static void main(String[] argv) throws Exception {
    String[] items = { "item1", "item2" };
    JComboBox cb = new JComboBox(items);
    cb.removeItemAt(0);
  }
}

Remove the last item

import javax.swing.JComboBox;
public class Main {
  public static void main(String[] argv) throws Exception {
    String[] items = { "item1", "item2" };
    JComboBox cb = new JComboBox(items);
    cb.removeItemAt(cb.getItemCount() - 1);
  }
}

Selecting an Item in a JComboBox Component with Multiple Keystrokes

import javax.swing.ruboBoxModel;
import javax.swing.JComboBox;
public class Main {
  public static void main(String[] argv) throws Exception {
    String[] items = { "A", "A", "B", "B", "C", "C" };
    JComboBox cb = new JComboBox(items);
    cb.setKeySelectionManager(new MyKeySelectionManager());
  }
}
class MyKeySelectionManager implements JComboBox.KeySelectionManager {
  long lastKeyTime = 0;
  String pattern = "";
  public int selectionForKey(char aKey, ComboBoxModel model) {
    int selIx = 01;
    Object sel = model.getSelectedItem();
    if (sel != null) {
      for (int i = 0; i < model.getSize(); i++) {
        if (sel.equals(model.getElementAt(i))) {
          selIx = i;
          break;
        }
      }
    }
    long curTime = System.currentTimeMillis();
    if (curTime - lastKeyTime < 300) {
      pattern += ("" + aKey).toLowerCase();
    } else {
      pattern = ("" + aKey).toLowerCase();
    }
    lastKeyTime = curTime;
    for (int i = selIx + 1; i < model.getSize(); i++) {
      String s = model.getElementAt(i).toString().toLowerCase();
      if (s.startsWith(pattern)) {
        return i;
      }
    }
    for (int i = 0; i < selIx; i++) {
      if (model.getElementAt(i) != null) {
        String s = model.getElementAt(i).toString().toLowerCase();
        if (s.startsWith(pattern)) {
          return i;
        }
      }
    }
    return -1;
  }
}

Setting ComboBox Editor and ComboBox Renderer

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.ruponent;
import java.awt.Dimension;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.ruboBoxEditor;
import javax.swing.DefaultListCellRenderer;
import javax.swing.JButton;
import javax.swing.JColorChooser;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JList;
import javax.swing.ListCellRenderer;
import javax.swing.border.LineBorder;
import javax.swing.event.EventListenerList;
class ColorComboBoxEditor implements ComboBoxEditor {
  final protected JButton editor;
  protected EventListenerList listenerList = new EventListenerList();
  public ColorComboBoxEditor(Color initialColor) {
    editor = new JButton("");
    editor.setBackground(initialColor);
    ActionListener actionListener = new ActionListener() {
      public void actionPerformed(ActionEvent e) {
        Color currentBackground = editor.getBackground();
        Color color = JColorChooser.showDialog(editor, "Color Chooser", currentBackground);
        if ((color != null) && (currentBackground != color)) {
          editor.setBackground(color);
          fireActionEvent(color);
        }
      }
    };
    editor.addActionListener(actionListener);
  }
  public void addActionListener(ActionListener l) {
    listenerList.add(ActionListener.class, l);
  }
  public Component getEditorComponent() {
    return editor;
  }
  public Object getItem() {
    return editor.getBackground();
  }
  public void removeActionListener(ActionListener l) {
    listenerList.remove(ActionListener.class, l);
  }
  public void selectAll() {
  }
  public void setItem(Object newValue) {
    if (newValue instanceof Color) {
      Color color = (Color) newValue;
      editor.setBackground(color);
    } else {
      try {
        Color color = Color.decode(newValue.toString());
        editor.setBackground(color);
      } catch (NumberFormatException e) {
      }
    }
  }
  protected void fireActionEvent(Color color) {
    Object listeners[] = listenerList.getListenerList();
    for (int i = listeners.length - 2; i >= 0; i -= 2) {
      if (listeners[i] == ActionListener.class) {
        ActionEvent actionEvent = new ActionEvent(editor, ActionEvent.ACTION_PERFORMED, color
            .toString());
        ((ActionListener) listeners[i + 1]).actionPerformed(actionEvent);
      }
    }
  }
}
class ColorCellRenderer implements ListCellRenderer {
  protected DefaultListCellRenderer defaultRenderer = new DefaultListCellRenderer();
  // Width doesn"t matter as the combo box will size
  private final static Dimension preferredSize = new Dimension(0, 20);
  public Component getListCellRendererComponent(JList list, Object value, int index,
      boolean isSelected, boolean cellHasFocus) {
    JLabel renderer = (JLabel) defaultRenderer.getListCellRendererComponent(list, value, index,
        isSelected, cellHasFocus);
    if (value instanceof Color) {
      renderer.setBackground((Color) value);
    }
    if(cellHasFocus || isSelected){
      renderer.setBorder(new LineBorder(Color.DARK_GRAY));
    }else{
      renderer.setBorder(null);
    }
    
    renderer.setPreferredSize(preferredSize);
    return renderer;
  }
}
public class ColorComboBoxEditorRendererDemo {
  public static void main(String args[]) {
    Color colors[] = { Color.BLACK, Color.BLUE, Color.GREEN, Color.RED, Color.WHITE, Color.YELLOW };
    JFrame frame = new JFrame("Color JComboBox");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    final JComboBox comboBox = new JComboBox(colors);
    comboBox.setEditable(true);
    comboBox.setRenderer(new ColorCellRenderer());
    Color color = (Color) comboBox.getSelectedItem();
    ComboBoxEditor editor = new ColorComboBoxEditor(color);
    comboBox.setEditor(editor);
    frame.add(comboBox, BorderLayout.NORTH);
    final JLabel label = new JLabel();
    label.setOpaque(true);
    label.setBackground((Color) comboBox.getSelectedItem());
    frame.add(label, BorderLayout.CENTER);
    ActionListener actionListener = new ActionListener() {
      public void actionPerformed(ActionEvent actionEvent) {
        Color selectedColor = (Color) comboBox.getSelectedItem();
        label.setBackground(selectedColor);
      }
    };
    comboBox.addActionListener(actionListener);
    frame.setSize(300, 200);
    frame.setVisible(true);
  }
}

Setting the Number of Visible Items in the Menu of a JComboBox Component

import javax.swing.JComboBox;
public class Main {
  public static void main(String[] argv) throws Exception {
    String[] items = new String[50];
    for (int i = 0; i < items.length; i++) {
      items[i] = "" + Math.random();
    }
    JComboBox cb = new JComboBox(items);
    // Retrieve the current max visible rows
    int maxVisibleRows = cb.getMaximumRowCount();
    // Change the current max visible rows
    maxVisibleRows = 20;
    cb.setMaximumRowCount(maxVisibleRows);
  }
}

Sharing the Data Model between two JComboBoxes

import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.DefaultComboBoxModel;
import javax.swing.JButton;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class SharedDataBetweenComboBoxSample {
  public static void main(String args[]) {
    final String labels[] = { "A", "B", "C", "D", "E", "F", "G" };
    final DefaultComboBoxModel model = new DefaultComboBoxModel(labels);
    JFrame frame = new JFrame("Shared Data");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    JPanel panel = new JPanel();
    JComboBox comboBox1 = new JComboBox(model);
    comboBox1.setEditable(true);
    JComboBox comboBox2 = new JComboBox(model);
    comboBox2.setEditable(true);
    panel.add(comboBox1);
    panel.add(comboBox2);
    frame.add(panel, BorderLayout.NORTH);
    JButton button = new JButton("Add");
    frame.add(button, BorderLayout.SOUTH);
    ActionListener actionListener = new ActionListener() {
      public void actionPerformed(ActionEvent actionEvent) {
        model.addElement("New Added");
      }
    };
    button.addActionListener(actionListener);
    frame.setSize(300, 200);
    frame.setVisible(true);
  }
}