How to handle more than two combobox

[Swela Jathar]

Hi,

I have 4 combo box and m adding values to combo box depending on previous combo box value.
n when user selects another value in same combo box i just called removeAllItems(); on combo box.so that previous values gets deleted. .it is working for only 2 combo boxes.
but it gives null pointer exception for more than 2 combo box. This is because when i called removeallItems() then actionlister is called automatically. n i hav written query for adding values to that in actionlistener.
so how should i handle these combo boxes??
thanks in advance...

[Greg Brannon]

Can you show some code?

[Swela Jathar]

Thanks Greq,

see I have combo boxs for Person Name,Person Id,and Receipt No.

I have added person names to combo in constructor.

 try
        {
            Statement kt=conn.createStatement();
            String p="SELECT DISTINCT c_name_of_person FROM watersupply order by c_name_of_person asc";
            ResultSet rt=kt.executeQuery(p);
                  while(rt.next())
                {


                  String get_cust=rt.getString("c_name_of_person");

                  combo_person_report.addItem(get_cust);

                 }
        }
        catch(Exception e)
        {
            e.printStackTrace();
        }

Next In ActionListener of first combo box i hav added customer id into 2nd combo box.
like

try
        {
            combo_person_id.removeAllItems();  
            String str_cust_report=combo_person_report.getSelectedItem().toString();
            Statement lt=conn.createStatement();
            String j="select n_customer_id,c_name_of_person from watersupply where c_name_of_person='"+str_cust_report+"'";
            ResultSet nt=lt.executeQuery(j);
               while(nt.next())
               {
                     int cs_id=nt.getInt("n_customer_id");
                    String str_cs_id=Integer.toString(cs_id);
                   combo_person_id.addItem(str_cs_id);
               }

        }
        catch(Exception e)
        {
            e.printStackTrace();
        }

up to this it is working fine...then according to customer id i wants to select receipt no.
so in actionlistener of 2nd combo box i hav written code like

     private void combo_person_idActionPerformed(java.awt.event.ActionEvent evt) {
  try
        {
             combo_receipt_report.removeAllItems();  //HERE IT GIVES NULL POINTER EXCEPTION
            
             String str_cust_report=combo_person_id.getSelectedItem().toString();

            Statement lt=conn.createStatement();
            String j="select distinct n_sr_no from watersupply where n_customer_id='"+str_cust_report+"'";
            ResultSet nt=lt.executeQuery(j);
                  while(nt.next())
                {
                     int receipt_no=nt.getInt("n_sr_no");
                    combo_receipt_report.addItem(receipt_no);
                }
            
        }
        catch(Exception e)
        {
            e.printStackTrace();
        }

}

I got Null pointer exception..

[Maneesh Godbole]

Where have you initialized combo_receipt_report?

[Swela Jathar]

thanks maneesh,
I have just added an item like "select report" in constructor...

combo_receipt_report.addItem("select report");

Main problem is that when i remove items from combo_receipt_report in combo_person_idActionPerformed (LINE NO 4) then actionlistener of combo_receipt_report is called.thats why it is giving null pointer exception..

Thanks...

[Ranganathan Kaliyur Mannar]

That indicates a problem in the actionListener code of combo_receipt_report. Based on your other actionListeners, I am thinking you are making a call to:

combo_receipt_report.getSelectedItem().toString(); 

in the actionListener of that combo. Instead you should add a null check. When all the items are removed, there is no item to select - so the getSelectedItem() will return null.

[Maneesh Godbole]

Swela Jathar wrote:thanks maneesh,
I have just added an item like "select report" in constructor...

combo_receipt_report.addItem("select report");

Main problem is that when i remove items from combo_receipt_report in combo_person_idActionPerformed (LINE NO 4) then actionlistener of combo_receipt_report is called.thats why it is giving null pointer exception..

Thanks...

I don't think you are understanding what I am saying. Have you initialized combo_receipt_report? Something like combo_receipt_report=new JComboBox()

[Swela Jathar]

ya..i hav initialized it...n then added item to it..

[Maneesh Godbole]

With the code you have posted till now it is difficult to say what's going wrong. You can help us help you better by posting a SSCCE code. Please do take out time to click the SSCCE link to find out what it really means.

[Andrew flexdeveloper]

Hi friends,

I also face the same problem.

Can you please help me in details?

[Swela Jathar]

Hi Maneesh,

can you show me some another example which handles more than three combo boxes?
Thanks..