Come determinare errori di java

Question

Sono solo un principiante Java. Avete qualche consiglio lì su come determinare gli errori. Sto cercando di connettersi a MySQL derby database. Non so come determinare l'errore, non c'è una linea rossa, ma c'è una finestra di messaggio che si presenta quando si tenta di eseguire il programma. Tutto quello che voglio fare è quello di visualizzare il primo record nel database. Tutto quello che ottiene è questo nell'output:

  

E: \ Users \ users.netbeans \ 6.8 \ var \ Cache \ esecutore-frammenti \ run.xml: 45:

package Employees;

import java.sql.Statement;

import javax.swing.JOptionPane;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.ResultSet;
/**
 *
 * @author Nrew
 */
public class Students extends javax.swing.JFrame {

    Connection con;
   Statement stmt;
   ResultSet rs;


    /** Creates new form Students */
    public Students() {
        initComponents();

DoConnect();

    }

    public void DoConnect(){
          try {
            String host= "jdbc:derby://localhost:1527/YURA";
String uname = "bart";
String pword = "12345";
con = DriverManager.getConnection(host, uname, pword);

 stmt = con.createStatement( );
String SQL = "SELECT * FROM APP.XROSS";
 rs = stmt.executeQuery(SQL);
rs.next();

rs.next( );
int ids = rs.getInt("IDNUM");
String idz = Integer.toString(ids);
String fname = rs.getString("FNAME");
String lname = rs.getString("LNAME");
String course = rs.getString("COURSE");
String skul = rs.getString("SCHOOL");
String gen = rs.getString("GENDER");

TextIDNUM.setText(idz);
TextFNAME.setText(fname);
TextLNAME.setText(lname);
textCOURSE.setText(course);
textSCHOOL.setText(skul);
textGENDER.setText(gen);







        }
        catch (SQLException err) {
          JOptionPane.showMessageDialog(Students.this, err.getMessage());



    }
    }

    /** This method is called from within the constructor to
     * initialize the form.
     * WARNING: Do NOT modify this code. The content of this method is
     * always regenerated by the Form Editor.
     */
    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">
    private void initComponents() {

        TextIDNUM = new javax.swing.JTextField();
        TextFNAME = new javax.swing.JTextField();
        TextLNAME = new javax.swing.JTextField();
        textCOURSE = new javax.swing.JTextField();
        textSCHOOL = new javax.swing.JTextField();
        textGENDER = new javax.swing.JTextField();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addGap(116, 116, 116)
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.TRAILING, false)
                    .addComponent(textGENDER, javax.swing.GroupLayout.Alignment.LEADING)
                    .addComponent(textSCHOOL, javax.swing.GroupLayout.Alignment.LEADING)
                    .addComponent(textCOURSE, javax.swing.GroupLayout.Alignment.LEADING)
                    .addComponent(TextLNAME, javax.swing.GroupLayout.Alignment.LEADING)
                    .addComponent(TextFNAME, javax.swing.GroupLayout.Alignment.LEADING)
                    .addComponent(TextIDNUM, javax.swing.GroupLayout.Alignment.LEADING, javax.swing.GroupLayout.DEFAULT_SIZE, 151, Short.MAX_VALUE))
                .addContainerGap(243, Short.MAX_VALUE))
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addGap(37, 37, 37)
                .addComponent(TextIDNUM, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addGap(18, 18, 18)
                .addComponent(TextFNAME, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addGap(18, 18, 18)
                .addComponent(TextLNAME, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addGap(18, 18, 18)
                .addComponent(textCOURSE, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
                .addComponent(textSCHOOL, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
                .addComponent(textGENDER, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addContainerGap(67, Short.MAX_VALUE))
        );

        pack();
    }// </editor-fold>

    /**
    * @param args the command line arguments
    */
    public static void main(String args[]) {
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new Students().setVisible(true);
            }
        });
    }

    // Variables declaration - do not modify
    private javax.swing.JTextField TextFNAME;
    private javax.swing.JTextField TextIDNUM;
    private javax.swing.JTextField TextLNAME;
    private javax.swing.JTextField textCOURSE;
    private javax.swing.JTextField textGENDER;
    private javax.swing.JTextField textSCHOOL;
    // End of variables declaration

}

Answer 1

stampare l'stackTrace in questo modo:

catch (SQLException err) {
    err.printStackTrace();  // <-- add this

    JOptionPane.showMessageDialog(Students.this, err.getMessage());
}