Java lang NullPointerException error

[Anand Karia]

Below is the function that i m using on two scnerio.

1st Scnerio.
=============
Just click on add button make entry into required fields and click Save Button.

I call this function before saving data into database. If i am calling this function within the form (Class A) then it is working fine and good.

2nd Scnerio
===========
I have 3 classes i.e. Class A, Class B and Class C

While working on Class A i am calling Class B and filling all kind of required data from Class B to global vector in Class C. After setting data from Class B to another Class C via vector, I close down Class B and again going to Class A as it is already opened.

On clicking a single button in Class A to fill my JTable from Class C (Vector), my all data is appearing and working fine.

But while saving as the below function is called i got an error on "Statement" statement i.e. Java.lang.NullPointerException.

System.out.println("Test");
This is not printed.

Can any one tell me why I am getting this error as the same is working in 1st Scnario.

  
private void getMaxValue(){
        try{
            String maxN = "Select  max(id) +1 from abcTable";
            System.out.println(maxN);
            Statement st = cnnd.myDetailCon.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,ResultSet.CONCUR_UPDATABLE );
            System.out.println("Test");
            ResultSet rsMaxVal = st.executeQuery(maxN);
            if (rsMaxVal.next() ==false) {
                txtSerial.setText("1");
            }
            else{    txtSerial.setText(rsMaxVal.getString(1));
            }
        }
        catch (Exception e) {
            lblStatus.setText("Max value not found");
            //System.out.println("Max value not found");
            msg.showMessageDialog(frame," " + lblCurrentUser.getText() + " !!! " + e,"ERROR",msg.WARNING_MESSAGE  );
        }
    }
 

[Keith Lynn]

It looks the problem may be with your connection.

cnnd.myDetailCon.

Before you try that line, try printing cnnd with System.out.println(cnnd) to see if it's null.

[Stefan Wagner]

It's generally a bad practise to catch any unspecific Exception:

 catch (Exception e) {

Instead catch specific (SQL...) Exceptions.

[Anand Karia]

Thanks Keith Lynn

You were right. Problem was there. I mistakenly close the connection from Class C.

Thanks anyway.

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