What is causing NullPointerException?

Question

I don't know why I am having null despite comparing the code to the ones I've written before.

This is my Java code to insert data into table:

  @FXML
    private void rewards_Parameters(){
        try{
            String sql = "INSERT INTO SetUpReward VALUES(?,?,?,?,?,?)";
            if(sql !=null){
                pst =con.prepareStatement(sql);
                pst.setString(2, txt_minGiftValue.getText());
                pst.setString(3, txt_maxGiftValue.getText());
                pst.setString(4, txt_RewardPoint.getText());

                pst.execute();
            }
        }catch(SQLException e){
            JOptionPane.showMessageDialog(null, e);
        }    
    }

My Init process...

 /**
 * FXML Controller class
 *
 * @author JIDO
 */
public class IGisftCardController implements Initializable {
    Connection con =null;
    ResultSet rs = null;
  PreparedStatement pst ;

Stacktrace:

Caused by: 

java.lang.NullPointerException
    at view_controller.IGisftCardController.loadReward(IGisftCardController.java:249)
    at view_controller.IGisftCardController.initialize(IGisftCardController.java:168)
    at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2548)
    ... 22 more
Exception running application igiftcardfx.IGiftCardFX
Java Result: 1

You provide neither part of the code where the exception occures and where you initialize your variables to non-null values... — Dici, Jul 11 '15 at 00:01
It's not specific to SO, it's about explaining a technical problem to someone. — Dici, Jul 11 '15 at 02:25

score 1 · Accepted Answer · answered Jul 10 '15 at 23:52

Because con is null. You test sql != null, make that con. And you should probably connect to a database (or at least log that you aren't). Also, please capture stack traces (they're invaluable for debugging your application). Something like,

String sql = "INSERT INTO SetUpReward VALUES(?,?,?,?,?,?)";
try {
    if (con != null) {
        pst = con.prepareStatement(sql);
        pst.setString(2, txt_minGiftValue.getText());
        pst.setString(3, txt_maxGiftValue.getText());
        pst.setString(4, txt_RewardPoint.getText());
        pst.setString(5, txt_CardNumber.getText());
        pst.setString(6, txt_PayPalEmail.getText());
        pst.setString(7, txt_BankName.getText());
        pst.setString(8, txt_BankAccount.getText());
        pst.execute();
    } else {
        System.out.println("No connection");
    }
} catch (SQLException e) {
    JOptionPane.showMessageDialog(null, e);
    e.printStackTrace();
}

Yup, you fixed one bug there, but the exception does not seem to happen in this method. — Dici, Jul 11 '15 at 00:03

What is causing NullPointerException?

1 Answers1