java JComboBox的事件处理

import java.awt.Container; import java.awt.Font; import java.awt.GridLayout; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import java.awt.event.ItemEvent; import java.awt.event.ItemListener; import java.awt.event.WindowAdapter; import java.awt.event.WindowEvent; import javax.swing.BorderFactory; import javax.swing.ComboBoxEditor; import javax.swing.JComboBox; import javax.swing.JFrame; import javax.swing.JLabel; public class JComboBoxDemo6 implements ItemListener, ActionListener { String[] fontsize = { "12", "14", "16", "18", "20", "22", "24", "26", "28" }; String defaultMessage = "请选择或直接输入文字大小!"; Font font = null; // 定义一个Font对象 JComboBox combo = null;// 定义一个JComboBox对象 JLabel label = null; // 定义一个JLabel对象 public JComboBoxDemo6() { JFrame f = new JFrame("JComboBox"); Container contentPane = f.getContentPane(); contentPane.setLayout(new GridLayout(2, 1)); label = new JLabel("Swing", JLabel.CENTER); font = new Font("SansSerif", Font.PLAIN, 12); label.setFont(font); combo = new JComboBox(fontsize); combo.setBorder(BorderFactory.createTitledBorder("请选择你要的文字大小:")); combo.setEditable(true); // 设置状态为可编辑 ComboBoxEditor editor = combo.getEditor(); combo.configureEditor(editor, defaultMessage); combo.addItemListener(this); // 添加文本监听 combo.addActionListener(this);// 添加事件监听 contentPane.add(label); contentPane.add(combo); f.pack(); f.show(); f.addWindowListener(new WindowAdapter() { public void windowClosing(WindowEvent e) { System.exit(0); } }); } public static void main(String[] args) { new JComboBoxDemo6(); } public void actionPerformed(ActionEvent e) { boolean isaddItem = true; int fontsize = 0; String tmp = (String) combo.getSelectedItem(); // 判断用户所输入的项目是否有重复，若有重复则不增加到JComboBox中。 try { fontsize = Integer.parseInt(tmp); for (int i = 0; i < combo.getItemCount(); i++) { if (combo.getItemAt(i).equals(tmp)) { isaddItem = false; break; } } if (isaddItem) { combo.insertItemAt(tmp, 0);// 插入项目tmp到0索引位置(第一列中). } font = new Font("SansSerif", Font.PLAIN, fontsize); label.setFont(font); } catch (NumberFormatException ne) { combo.getEditor().setItem("你输入的值不是整数值，请重新输入!"); } } public void itemStateChanged(ItemEvent e) {// ItemListener界面只有itemStateChanged()一个方法，在此实作它。 if (e.getStateChange() == ItemEvent.SELECTED) {// 当用户的选择改变时，则在JLabel上会显示出Swing目前字形大小信息. int fontsize = 0; try { fontsize = Integer.parseInt((String) e.getItem()); label.setText("Swing 目前字形大小:" + fontsize); } catch (NumberFormatException ne) {// 若所输入的值不是整数，则不作任何的操作. } } } }