问答题 下面是实现用户界面程序的一个例子，请在画线处填写适当语句，使程序能正确执行。 import javax.swing.JFileChooser; import javax.swing.JTextArea; import javax.swing.JButton; import javax.swing.JFrame; import javax.swing.JPanel; import java.awt.event.*; import java.io.*; import java.awt.*; public class SwingExample3 implements ActionListener{ private JFrame frame; private JButton button; private JButton saveButton; private JTextArea textArea; private JFileChooser dia; private JPanel buttonPanel; public void initGUI(){ frame=new JFrame("file chooser"); button=new JButton("open file"); button.setActionCommand("open"); button.addActionListener(this); saveButton=new JButton("save file")； saveButton.setActionCommand("save"); saveButton.addActionListener(this); textArea=new JTextArea(" ",10,10); buttonPanel=new JPanel(); dia=new JFileChooser(); frame.addWindowListener(new WindowAdapter(){ public void windowClosing(WindowEvent e){ System.exit(0);} }); buttonPanel.add(button); buttonPanel.add(saveButton); frame.getContentPane().add(buttonPanel,BorderLayout.NORTH); frame.getContentPane().add(textArea,BorderLayout.CENTER); frame.setSize(200,200); frame.setVisible(true); public void actionPerformed(ActionEvent event){ if(event.getActionCommand().equals("open")){ //打开文件 dia.showOpenDialog(frame); dia.setVisible(true); File file=dia.getSelectedFile(); String fileName=file.getAbsolutePath(); textArea.append("path of selected file:"+fileName+"/r/n"); } else if(event.getActionCommand().equals("save")){ //保存文件 dia.______; dia.setVisible(true); File file=dia.getSelectedFile(); String fileName=file.getAbsolutePath(); textArea.append("path of saved file:"+fileName+"/r/n"); } } public static void main(String args[]){ swingExample3 example=new swingExample3(); example.initGUI(); } }