JComboBox

Swinging Duke

Swing creates and manages combo boxes using the JComboBox class, which implements a classic combo box. You can also create customized combo boxes using the JComboBox class.

JComboBox shares the following features with other kinds of list boxes:

Generic display: JComboBox uses the ListCellRenderer interface to display any kind of object for both the selected value and the list of possible values.
ListSelectionModel: JComboBox implements the ListSelectionModel interface.
List Selection events: JComboBox uses the ListSelectionEvent class to determine when a list item is selected. A ListSelection event is an event that is fired by a change in the current selection. This change is limited to a row interval. When a ListSelectionEvent is detected, a ListSelectionListener generally queries the source of the event to retrieve the new selected status of each potentially changed row. For more details, see the ListSelectionEvent, ListSelectionListener, and ListSelectionModel APIs.
Support for editing: To make the items in a combo box editable, you call a method named setEditable(), using a true parameter, as follows:

    cb.setEditable(true);

The following code fragment shows how a classic combo box can be implemented in a program that makes use of Swing. The example comes from a source file named ComboBoxPanel.java, which is part of the SwingSet sample program that is distributed with Swing. The code creates a classic combo box, an editable combo box, and a customized combo box with an item list that can be manipulated using tree-node operations:

    public ComboBoxPanel(SwingSet swing) {
      JPanel tp;
      this.swing = swing;
      this.setLayout(new BoxLayout(this,BoxLayout.Y_AXIS));
      setBorder(swing.emptyBorder5);
      
      this.add(Box.createRigidArea(new Dimension(1,50)));
      JPanel panel = new JPanel(false);
      panel.setLayout(new BoxLayout(panel,BoxLayout.X_AXIS));
      add(panel);
      // Classic combo box
      tp = new JPanel();
      tp.setMaximumSize(new Dimension(Short.MAX_VALUE,100));
      tp.setBorder(BorderFactory.createTitledBorder
        ("Classic ComboBox"));
		// tp.setTitle("Classic ComboBox");
      tp.setLayout(new BoxLayout(tp,BoxLayout.X_AXIS));
      tp.add(Box.createRigidArea(new Dimension(5,1)));
      months = new JComboBox();
      months.addItem("January");
      months.addItem("February");
      months.addItem("March");
      months.addItem("April");
      months.addItem("May");
      months.addItem("June");
      months.addItem("July");
      months.addItem("August");
      months.addItem("September");
      months.addItem("October");
      months.addItem("November");
      months.addItem("December");
      tp.add(months);
      tp.add(Box.createRigidArea(new Dimension(5,1)));
      days = new JComboBox();
      days.addItem("Monday");
      days.addItem("Tuesday");
      days.addItem("Wednesday");
      days.addItem("Thursday");
      days.addItem("Friday");
      days.addItem("Saturday");
      days.addItem("Sunday");
      tp.add(days);
      tp.add(Box.createRigidArea(new Dimension(5,1)));
      panel.add(tp);

      // Editable combo box

      add(panel);
      tp = new JPanel();
      tp.setMaximumSize(new Dimension(Short.MAX_VALUE,100));
      tp.setBorder(BorderFactory.createTitledBorder("Editable ComboBox"));
      tp.setLayout(new BoxLayout(tp,BoxLayout.X_AXIS));
      tp.add(Box.createRigidArea(new Dimension(5,1)));
      cb = new JComboBox();
      cb.setEditable(true);
      cb.addItem("0");
      cb.addItem("10");
      cb.addItem("20");
      cb.addItem("30");
      cb.addItem("40");
      cb.addItem("50");
      cb.addItem("60");
      cb.addItem("70");
      cb.addItem("80");
      cb.addItem("90");
      cb.addItem("100");
      cb.addItem("More");
      cb.setSelectedItem("50");
      tp.add(cb);
      tp.add(Box.createRigidArea(new Dimension(5,1)));

      cb1 = new JComboBox();
      cb1.setEditable(true);
      cb1.addItem("0");
      cb1.addItem(".25");
      cb1.addItem(".5");
      cb1.addItem(".75");
      cb1.addItem("1.0");
      cb1.setSelectedItem(".5");
      tp.add(cb1);

      tp.add(Box.createRigidArea(new Dimension(5,1)));
      panel.add(tp);

      // Custom combobox
      panel = new JPanel(false);
      panel.setLayout(new BoxLayout(panel,BoxLayout.X_AXIS));
      add(panel);
      tp = new JPanel();
      tp.setMaximumSize(new Dimension(Short.MAX_VALUE,200));
      tp.setBorder(BorderFactory.createTitledBorder("Custom ComboBox"));
		// tp.setTitle("Custom ComboBox");
      tp.setLayout(new BoxLayout(tp,BoxLayout.X_AXIS));
      tp.add(Box.createRigidArea(new Dimension(5,1)));
      custom = new CustomComboBox(new CustomComboBoxModel());
      custom.setRenderer(new TestCellRenderer(custom));
      ((CustomComboBox)custom).setCanChangeRenderer(false);
      custom.setSelectedItemIndex(0);
      custom.setMaximumRowCount(4);
      tp.add(custom);
      tp.add(Box.createRigidArea(new Dimension(5,1)));

      DefaultMutableTreeNode swingNode = new DefaultMutableTreeNode("Swing");
      DefaultMutableTreeNode spec  = new DefaultMutableTreeNode("spec");
      DefaultMutableTreeNode api   = new DefaultMutableTreeNode("api");

      swingNode.add(spec);
      swingNode.add(api);

      api.add(new DefaultMutableTreeNode("JComponent"));
      api.add(new DefaultMutableTreeNode("JTable"));
      api.add(new DefaultMutableTreeNode("JTree"));
      api.add(new DefaultMutableTreeNode("JComboBox"));
      api.add(new DefaultMutableTreeNode("JTextComponent"));

      spec.add(new DefaultMutableTreeNode("JComponent"));
      spec.add(new DefaultMutableTreeNode("JTable"));
      spec.add(new DefaultMutableTreeNode("JTree"));
      spec.add(new DefaultMutableTreeNode("JComboBox"));
      spec.add(new DefaultMutableTreeNode("JTextComponent"));
      
      treeComboBox = new TreeCombo(new DefaultTreeModel(swingNode));
      tp.add(treeComboBox);
      tp.add(Box.createRigidArea(new Dimension(5,1)));
      panel.add(tp);
    }

More comprehensive documentation for the JComboBox class in now being developed. Meanwhile, you can learn more about how the BorderFactory works by consulting the JComboBox API and by examing the code in the SwingSet sample application.