Question

这是我输入的代码

// loading all distict age on to list bix from student table
 private void b1ActionPerformed(java.awt.event.ActionEvent evt) {                                   
DefaultTableModel tb = (DefaultTableModel)tb1.getModel();
tb.setRowCount(0);
String sql = "select * from student";
try
{
Class.forName("java.sql.Driver");
Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/info","root","");  
Statement s = con.createStatement();
ResultSet rs = s.executeQuery(sql);
while(rs.next())
{
    int s_rno = rs.getInt(1);
    String s_name = rs.getString(2);
    int s_age = rs.getInt(3);
    double s_marks = rs.getDouble(4);
    tb.addRow(new Object[]{s_rno, s_name, s_age, s_marks});
    tb1.setModel(tb);
}
rs.close();
s.close();
con.close();
}
catch(Exception e)
{
    JOptionPane.showMessageDialog(this, e.getMessage());
}        
}

当我运行程序时，会出现GUI，但是在按下按钮时，没有任何反应，并且我的输出窗口出现以下错误

线程“AWT-EventQueue-0”中的异常java.lang.ClassCastException： JDBC2 $ 2无法强制转换为javax.swing.DefaultListModel at JDBC2.b1ActionPerformed（JDBC2.java:74）at JDBC2.access $ 000（JDBC2.java:9）at JDBC2 $ 1.actionPerformed（JDBC2.java:36）at javax.swing.AbstractButton.fireActionPerformed（AbstractButton.java:2022）在 javax.swing.AbstractButton中的$ Handler.actionPerformed（AbstractButton.java:2348）在 javax.swing.DefaultButtonModel.fireActionPerformed（DefaultButtonModel.java:402）在 javax.swing.DefaultButtonModel.setPressed（DefaultButtonModel.java:259）在 javax.swing.plaf.basic.BasicButtonListener.mouseReleased（BasicButtonListener.java:252）在java.awt.Component.processMouseEvent（Component.java：6535）at javax.swing.JComponent.processMouseEvent（JComponent.java:3324）at java.awt.Component.processEvent（Component.java:6300）at java.awt.Container.processEvent（Container.java:2236）at java.awt.Component.dispatchEventImpl（Component.java:4891）at java.awt.Container.dispatchEventImpl（Container.java:2294）at java.awt.Component.dispatchEvent（Component.java:4713）at java.awt.LightweightDispatcher.retargetMouseEvent（Container.java:4888）在 java.awt.LightweightDispatcher.processMouseEvent（Container.java:4525） at java.awt.LightweightDispatcher.dispatchEvent（Container.java:4466）在java.awt.Container.dispatchEventImpl（Container.java:2280）at java.awt.Window.dispatchEventImpl（Window.java:2750）at java.awt.Component.dispatchEvent（Component.java:4713）at java.awt.EventQueue.dispatchEventImpl（EventQueue.java:758）at at java.awt.EventQueue.access $ 500（EventQueue.java:97）at java.awt.EventQueue $ 3.run（EventQueue.java:709）at java.awt.EventQueue $ 3.run（EventQueue.java:703）at java.security.AccessController.doPrivileged（Native Method）at java.security.ProtectionDomain $ JavaSecurityAccessImpl.doIntersectionPrivilege（ProtectionDomain.java:76）在 java.security.ProtectionDomain $ JavaSecurityAccessImpl.doIntersectionPrivilege（ProtectionDomain.java:86）在java.awt.EventQueue $ 4.run（EventQueue.java:731）at java.awt.EventQueue $ 4.run（EventQueue.java:729）at java.security.AccessController.doPrivileged（Native Method）at java.security.ProtectionDomain $ JavaSecurityAccessImpl.doIntersectionPrivilege（ProtectionDomain.java:76）在java.awt.EventQueue.dispatchEvent（EventQueue.java:728）at java.awt.EventDispatchThread.pumpOneEventForFilters（EventDispatchThread.java:201）在 java.awt.EventDispatchThread.pumpEventsForFilter（EventDispatchThread.java:116）在 java.awt.EventDispatchThread.pumpEventsForHierarchy（EventDispatchThread.java:105）在 java.awt.EventDispatchThread.pumpEvents（EventDispatchThread.java:101）在 java.awt.EventDispatchThread.pumpEvents（EventDispatchThread.java:93）在java.awt.EventDispatchThread.run（EventDispatchThread.java:82）

我需要更多的帮助，我能理解错误。

Answer 1

看看第74行;必须是错误发生的地方。

处理动作事件时，您正在做一些繁重的工作。以下内容将invokeLater推迟一点，以便至少可以看到直接的GUI响应。

我已经纠正了表模型的用法。还会有太多的消息被解雇。

private void b1ActionPerformed(java.awt.event.ActionEvent evt) {
    SwingUtilities.invokeLater(new Runnable() {

        @Override
        public void run() {
            DefaultTableModel tb = (DefaultTableModel) tb1.getModel();
            tb.setRowCount(0);
            String sql = "select * from student";
            try (Connection con = DriverManager.getConnection("jdbc:...", "...", "");
                    Statement s = con.createStatement();
                    ResultSet rs = s.executeQuery(sql)) {
                while (rs.next()) {
                    int s_rno = rs.getInt(1);
                    String s_name = rs.getString(2);
                    int s_age = rs.getInt(3);
                    double s_marks = rs.getDouble(4);
                    tb.addRow(new Object[] { s_rno, s_name, s_age, s_marks });
                }
            } catch (SQLException e) {
                JOptionPane.showMessageDialog(this, e.getMessage());
            }
        }
    });
}

可能发生的地方是：

            DefaultTableModel tb = (DefaultTableModel) tb1.getModel();

（这条线是74？）

一般情况下，最好创建一个新的DefaultTableModel（AbstractTableModel？），并在方法结束时执行tb1.setModel(tb)。

顺便说一句，网络中已有针对ResultSet的TableModel。

Swing错误ClassCastException

1 个答案: