import java.awt.event.ItemListener; import java.awt.event.ItemEvent; import javax.swing.JFrame; import javax.swing.JComboBox; public class ComBoxDemo extends JFrame { JComboBox computer; //主类别下拉框 JComboBox fittings; //配件下拉框 public ComBoxDemo() { super("ComBoxDemo"); this.setLayout(null); computer=new JComboBox(new String[]{"", "联想电脑", "华硕笔记本", "IBM笔记本"}); fittings = new JComboBox(); //设置两个下拉框的位置和大小 computer.setBounds(100, 40, 100, 25); fittings.setBounds(100, 80, 100, 25); //添加事件监听器 computer.addItemListener(new ItemListener() { //设置几组常量保存各电脑品牌的配件信息 private final String[] ITEM_LX = {"联想CPU", "联想内存", "联想显示器"}; private final String[] ITEM_HS = {"华硕CPU", "华硕内存", "华硕液晶屏"}; private final String[] ITEM_IBM = {"IBMCPU", "IBM内存", "IBM液晶屏"}; //开始itemStateChanged方法，该方法在选择一台电脑时自动调用 public void itemStateChanged(ItemEvent e) { //首先获得选择的电脑品牌的索引号 int index = computer.getSelectedIndex(); //将配件下拉框中的所有项移除 fittings.removeAllItems(); //判断所选的电脑品牌 switch (index) { case 1: //联想电脑 addItems(ITEM_LX); break; case 2: //华硕笔记本 addItems(ITEM_HS); break; case 3: //IBM笔记本