JTextArea ta = new JTextArea(); JTextField txt = new JTextField(10);JFrame jf = new JFrame("功能界面"); jf.setBounds(0, 0, 700, 600); jf.setVisible(true); jf.setLayout(null); jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); JButton b1 = new JButton("图书入库"); b1.setBounds(20, 90, 150, 80); JButton b2 = new JButton("图书查询"); b2.setBounds(20, 210, 150, 80); JButton b3 = new JButton("图书修改"); b3.setBounds(500, 90, 150, 80); JButton b5 = new JButton("办理借阅证登记"); b5.setBounds(20, 330, 150, 80); JButton b6 = new JButton("图书借阅管理"); b6.setBounds(500, 210, 150, 80); JButton b4 = new JButton("图书删除"); b4.setBounds(500, 330, 150, 80); JButton b7 = new JButton("退出系统"); b7.setBounds(560, 20, 90, 30); ta.setBounds(190, 90, 290, 320); txt.setBounds(120,450,300,30); JButton b8 = new JButton("确定"); b8.setBounds(440,450,70,30); JMenuBar menuBar = new JMenuBar(); JMenu menuManage = new JMenu("图书管理"); JMenu menuAbout = new JMenu("关于系统"); JMenuItem item1 = new JMenuItem("图书列表"); menuManage.add(item1); item1.addActionListener(new ActionListener() { @Override public void actionPerformed(ActionEvent e) { JFrame frame = new JFrame("图书列表"); frame.setSize(600, 400); frame.setLocationRelativeTo(null); ListPanel listPanel = new ListPanel(); frame.add(listPanel); frame.setVisible(true); } }); ActionListener act = new ActionListener() { @Override public void actionPerformed(ActionEvent e) { if(e.getSource().equals(b1)) { insertNewbook(); }else if(e.getSource().equals(b3)) { updatebook(); }else if(e.getSource().equals(b4)) { ta.setText("请输入要删除的图书编号:\n"); String bid = txt.getText(); if(bid!=null && !bid.trim().equals("")) { ta.append(bid+"\n"); if(dbDao.delelteBook(bid)){ System.out.print("啥"+bid); int user = JOptionPane.showConfirmDialog(null, "图书删除成功","提示",JOptionPane.YES_NO_OPTION); }else{ int user = JOptionPane.showConfirmDialog(null, "图书删除失败","提示",JOptionPane.YES_NO_OPTION); } }else { ta.append("消息不能为空"+"\n"); } }public boolean delelteBook(String bid){ boolean flag=false; PreparedStatement pstmt=null; String sql="DELETE FROM booklist WHERE bid=?"; try{ pstmt=conn.prepareStatement(sql); pstmt.setString(1, bid); if (pstmt.executeUpdate() > 0) { flag = true; } } catch (SQLException e) { e.printStackTrace(); } finally { try { pstmt.close(); } catch (SQLException e) { e.printStackTrace(); } } return flag; }这是我的部分代码，我想要获取我输入的bid，调用删除图书方法后弹窗显示删除成功，但是出错了，请帮我改一下

在你的代码中，存在以下问题：

1. 删除图书方法的实现需要获取数据库连接对象，但是在代码中没有展示如何获取该连接对象。

2. 在删除图书方法中，应该将PreparedStatement对象声明在try语句块内，并在finally语句块中关闭该对象。

3. 在删除图书方法中，应该将ResultSet对象声明在try语句块内，并在finally语句块中关闭该对象。

4. 在删除图书方法中，应该将Connection对象声明在try语句块内，并在finally语句块中关闭该对象。

5. 在删除图书方法中，应该将PreparedStatement对象的执行结果作为返回值返回。

以下是修改后的代码：

JTextArea ta = new JTextArea();
JTextField txt = new JTextField(10);
JFrame jf = new JFrame("功能界面");
jf.setBounds(0, 0, 700, 600);
jf.setVisible(true);
jf.setLayout(null);
jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

JButton b1 = new JButton("图书入库");
b1.setBounds(20, 90, 150, 80);

JButton b2 = new JButton("图书查询");
b2.setBounds(20, 210, 150, 80);

JButton b3 = new JButton("图书修改");
b3.setBounds(500, 90, 150, 80);

JButton b5 = new JButton("办理借阅证登记");
b5.setBounds(20, 330, 150, 80);

JButton b6 = new JButton("图书借阅管理");
b6.setBounds(500, 210, 150, 80);

JButton b4 = new JButton("图书删除");
b4.setBounds(500, 330, 150, 80);

JButton b7 = new JButton("退出系统");
b7.setBounds(560, 20, 90, 30);

ta.setBounds(190, 90, 290, 320);

txt.setBounds(120,450,300,30);

JButton b8 = new JButton("确定");
b8.setBounds(440,450,70,30);

JMenuBar menuBar = new JMenuBar();

JMenu menuManage = new JMenu("图书管理");

JMenu menuAbout = new JMenu("关于系统");

JMenuItem item1 = new JMenuItem("图书列表");

menuManage.add(item1);

item1.addActionListener(new ActionListener() {
    @Override
    public void actionPerformed(ActionEvent e) {
        JFrame frame = new JFrame("图书列表");
        frame.setSize(600, 400);
        frame.setLocationRelativeTo(null);
        ListPanel listPanel = new ListPanel();
        frame.add(listPanel);
        frame.setVisible(true);
    }
});

ActionListener act = new ActionListener() {
    @Override
    public void actionPerformed(ActionEvent e) {
        if(e.getSource().equals(b1)) {
            insertNewbook();
        }else if(e.getSource().equals(b3)) {
            updatebook();
        }else if(e.getSource().equals(b4)) {
            ta.setText("请输入要删除的图书编号:\n");
            String bid = txt.getText();
            if(bid!=null && !bid.trim().equals("")) {
                ta.append(bid+"\n");
                if(deleteBook(bid)){
                    int user = JOptionPane.showConfirmDialog(null, "图书删除成功","提示",JOptionPane.YES_NO_OPTION);
                }else{
                    int user = JOptionPane.showConfirmDialog(null, "图书删除失败","提示",JOptionPane.YES_NO_OPTION);
                }
            }else {
                ta.append("消息不能为空"+"\n");
            }
        }
    }
};

public boolean deleteBook(String bid) {
    boolean flag=false;
    Connection conn=null;
    PreparedStatement pstmt=null;
    ResultSet rs = null;
    try{
        conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/test", "root", "123456");
        String sql="DELETE FROM booklist WHERE bid=?";
        pstmt=conn.prepareStatement(sql);
        pstmt.setString(1, bid);
        flag = pstmt.executeUpdate() > 0;
    } catch (SQLException e) {
        e.printStackTrace();
    } finally {
        try {
            if (rs != null) {
                rs.close();
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
        try {
            if (pstmt != null) {
                pstmt.close();
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
        try {
            if (conn != null) {
                conn.close();
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
    return flag;
}