问答题

本题程序的功能是监听对于列表项的操作。窗口中有一个列表和“添加”、“删除”和“关闭”三个按钮。单击“添加”按钮，会在当前所选列表项后添加一个名为“新增表项”的列表项，同时后台输入列表中的表项数量。单击“删除”按钮，如果未选中表项，则弹出提示消息框“请选择表项”，否则将选中的表项删除，同时后台输出删除表项的内容和列表中的表项数量。单击“关闭”按钮退出程序。程序中存在若干错误，请找出并改正(注意：不得改动程序的结构，不得增行或删行)。
import java.awt.*;
import java.awt.event.*;
import javax.swing.JOptionPane;
public class advance

public static void main(String args[])

final Frame frmFrame = new Frame();
Panel pnlPanel1 = new Panel();
Panel pnlPanel2 = new Panel();
final List istList = new List(8);
for(int i = 0; i ＜10; i++)

String strName = "表项" + (new Integer(i+1)).toString();
istList.add( strName );

Button btnButton1 = new Button("添加");
Button btnButton2 = new Button("删除");
Button btnButton3 = new Button("关闭");
btnButton1.addActionListener( new ActionListener()
publiC void actionPerformed(ActionEvent e)

lstList.add("新增表项",istList.getSelected()+1);
System.out.println("列表中的表项数量" + istList,getItemCount() );

);
btnButton2.addActionListener (new ActionListener ()
public void actionPerformed(ActionEvent e)

if(istList.getSelected() == null)

JOptionPane.showMessageDialog(frmFrame,"请选择表项");
return;

System.out.println("删除表项的内容:"+ istList,getSelectedItem());
istList.delete(istList.getSelectedIndex());
System.out.println("列表中的表项数量: " + istList,getItemCount ());

);
btnButton3.addActionListener(new ActionListener ()
public void actionPerformed(ActionEvent e)

System.exit (0);

);
pnlPanel1 .add (istList);
pnlPanel2 .add (btnButton1);
pnlPanel2 .add (btnButton2);
pnlPanel2,add (btnButton3);
frmFrame.add("North",pnlPanel1);
frmFrame.add("South",pnlPanel2);
frmFrame,setTitle ("advance");
frmFrame.pack ();
frmFrame,show ();