JTable : getting data from table

Question

I am trying to run this code .This contains a table which has 2 rows and 4 column and the table is for entering the marks of the student but i am constantly getting this error of nullpointer exception on line 353. Plzzz help me here is the code

    package uclidit;

    import java.sql.Connection;
    import java.sql.DriverManager;
    import java.sql.*;
    import javax.swing.JOptionPane;
    import javax.swing.table.DefaultTableModel;

     public class EdittedForm extends javax.swing.JFrame {
     String course,yearf,yeart, aggr;

    public EdittedForm() {
        initComponents();
    }


    @SuppressWarnings("unchecked")


    private void jButton2ActionPerformed(java.awt.event.ActionEvent evt) {                                         
        // TODO add your handling code here:
    }                                        

    private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
        // TODO add your handling code here
        getData();

        try{
        String url="jdbc:mysql://localhost:3306/entryform";
                Class.forName("com.mysql.jdbc.Driver");
                Connection con=DriverManager.getConnection(url,"root","root");
                String query="insert into 

     marks(course,yearf,yeart,sem1,sem2,sem3,sem4,sem5,sem6,sem7,sem8,aggregate)
               values(?,?,?,?,?,?,?,?,?,?,?,?)";
                PreparedStatement ps = con.prepareStatement(query);

                ps.setString(1,course);
               ps.setString(2,yearf);
                ps.setString(3,yeart);

                ps.setFloat(4,0);

               ps.setFloat(5,0);
                ps.setFloat(6,0);
                ps.setFloat(7,0);
                ps.setFloat(8, 0);
                ps.setFloat(9,0);
               ps.setFloat(10,0);
                ps.setFloat(11,0);
              ps.setString(12,aggr);

            ps.executeUpdate();


        }
        catch(Exception e){
            e.printStackTrace();
        }
    }                                        
          public void getData()
      {



    course = jTable1.getValueAt(0,0).toString();
    JOptionPane.showMessageDialog(this, course);
     yearf = jTable1.getValueAt(0,1).toString();
     JOptionPane.showMessageDialog(this,yearf );
     yeart=jTable1.getValueAt(0,2).toString();
     JOptionPane.showMessageDialog(this, yeart);
     aggr = jTable1.getValueAt(0,3).toString();
     JOptionPane.showMessageDialog(this, aggr);

     }

    public static void main(String args[]) {


        /* Create and display the form */
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new EdittedForm().setVisible(true);
            }
        });
    }

    // Variables declaration - do not modify                     
    private javax.swing.JButton jButton1;
    private javax.swing.JButton jButton2;
    private javax.swing.JScrollPane jScrollPane1;
    private javax.swing.JScrollPane jScrollPane2;
    private javax.swing.JScrollPane jScrollPane3;
    private javax.swing.JScrollPane jScrollPane4;
    private javax.swing.JScrollPane jScrollPane5;
    private javax.swing.JScrollPane jScrollPane6;
    private javax.swing.JScrollPane jScrollPane7;
    private javax.swing.JScrollPane jScrollPane8;
    private javax.swing.JScrollPane jScrollPane9;
    private javax.swing.JTable jTable1;
    private javax.swing.JTable jTable2;
    private javax.swing.JTable jTable3;
    private javax.swing.JTable jTable4;
    private javax.swing.JTable jTable5;
    private javax.swing.JTable jTable6;
    private javax.swing.JTable jTable7;
    private javax.swing.JTable jTable8;
    private javax.swing.JTable jTable9;
    // End of variables declaration                   
   }

and the error is

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at uclidit.EdittedForm.getData(EdittedForm.java:353)
at uclidit.EdittedForm.jButton1ActionPerformed(EdittedForm.java:316)
at uclidit.EdittedForm.access$000(EdittedForm.java:17)
at uclidit.EdittedForm$7.actionPerformed(EdittedForm.java:251)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018)

Answer 1

Is this the complete code? As far as I can see you declare jTable1 but you don't initialize it. So you have to prepare or create a jTable1 with

jTable1 = new JTable(data, columnNames);

where the constructors are

JTable(Object[][] rowData, Object[] columnNames) 
JTable(Vector rowData, Vector columnNames)

further information here: https://docs.oracle.com/javase/tutorial/uiswing/components/table.html

So I think that you get a null pointer exception at:

course = jTable1.getValueAt(0, 0).toString();

because jTable1 is null

Answer 2

As far as I can see, jtable1 isn't initialised. Make sure it is. If the error persists, it is because one of the getValue() calls in getData() returns null. You can use String.valueOf(jTable1.getValueAt(0,0)) instead of jTable1.getValueAt(0,0).toString() to avoid NullPointerException in that case.