我非常感谢那些回答我的问题“未找到主要方法错误”的人，在更正所有括号后，代码似乎没问题。在 IDE 上它仍然指示以下错误；
private javax.swing.JButton jButton1;
private javax.swing.JComboBox jComboBox1;
private javax.swing.JLabel jLabel1;
private javax.swing.JLabel jLabel2;
private javax.swing.JLabel jLabel3;
private javax.swing.JLabel jLabel4;
private javax.swing.JTextField jTextField1;
private javax.swing.JTextField jTextField2;
error line** private javax.swing.JTextField jTextField3;
即构建失败，指示上面唯一的错误行，因此，这些是 IDE 的变量声明，无法修改。
主要代码是；
private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {
try {
DriverManager.registerDriver(new org.apache.derby.jdbc.ClientDriver());
Connection conn=DriverManager.getConnection("jdbc:derby://localhost:1527/sample","app","app");
preparedStatement ps=conn.prepareStatement("select name,zip,discount_code from customer where customer_id=?");
ps.setInt(1,Interger.parseInt(jTextField1.getText()));
ResultSet rs=ps.executeQuery();
if(rs.next()) {
jTextField2.setText(rs.getString(1));
jTextField3.setText(rs.getString(2));
jComboBox1.setSelectedItem(rs.getString(3));
}
} catch (NumberFormatException ex) {
ex.PrintStackTrace();
}catch (SQLException ex){
ex.printStackTrace();
}
}
public static void main(String args[]) {
java.awt.EventQueue.invokeLater(new Runnable() {
public void run() {
new jdfrm().setVisible(true);
}