（2）指定这些对象在GUI中的显示方式。
您可以将任何Object添加到模型，然后创建一个自定义渲染器以任意方式显示该对象。显示toString（）方法和自定义渲染器方法的简单示例：
import java.awt.*;import java.awt.event.*;import java.util.*;import javax.swing.*;import javax.swing.plaf.basic.*;public class ComboBoxItem extends Jframe implements ActionListener{ public ComboBoxItem() { Vector model = new Vector(); model.addElement( new Item(1, "car" ) ); model.addElement( new Item(2, "plane" ) ); model.addElement( new Item(3, "train" ) ); model.addElement( new Item(4, "boat" ) ); JComboBox comboBox; // Easiest approach is to just override toString() method // of the Item class comboBox = new JComboBox( model ); comboBox.setDragEnabled(true); comboBox.addActionListener( this ); getContentPane().add(comboBox, BorderLayout.NORTH ); // Most flexible approach is to create a custom render // to diplay the Item data comboBox = new JComboBox( model ); comboBox.setDragEnabled(true); comboBox.setRenderer( new ItemRenderer() ); comboBox.addActionListener( this ); getContentPane().add(comboBox, BorderLayout.SOUTH ); } public void actionPerformed(ActionEvent e) { JComboBox comboBox = (JComboBox)e.getSource(); Item item = (Item)comboBox.getSelectedItem(); System.out.println( item.getId() + " : " + item.getDescription() ); } class ItemRenderer extends BasicComboBoxRenderer { public Component getListCellRendererComponent( JList list, Object value, int index, boolean isSelected, boolean cellHasFocus) { super.getListCellRendererComponent(list, value, index, isSelected, cellHasFocus); if (value != null) { Item item = (Item)value; setText( item.getDescription().toUpperCase() ); } if (index == -1) { Item item = (Item)value; setText( "" + item.getId() ); } return this; } } class Item { private int id; private String description; public Item(int id, String description) { this.id = id; this.description = description; } public int getId() { return id; } public String getDescription() { return description; } public String toString() { return description; } } public static void main(String[] args) { Jframe frame = new ComboBoxItem(); frame.setDefaultCloseOperation( EXIT_ON_CLOSE ); frame.pack(); frame.setVisible( true ); }}
