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NULL Pointer Exception

Posted on 2004-04-26
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Last Modified: 2012-06-27
Objective: select all columns in a table for the selected item in the JComboBox that matches a table number in a table,
                use values  from table for JTextFields, call displayTotal meth with column called subtotal from table in dbase

Thanks......


 private void tableNumberJComboBoxItemStateChanged(
      ItemEvent event )
   {
            String waiter="";
            int tableNum = 0;
            double subT = 0.0;
;

            //query db for all columns for selected item from jcombobox
            try
            {
                  //select all columns from restaurantTable table
                  myRS=mySt.executeQuery( "select * from restauranttables " +
                  "where tablenumber = " + ItemEvent.SELECTED );


                  while( myRS.next() )
                  {
                              //match waiter name to table number
                              waiter = ( myRS.getString ( "waitername" ));
                              tableNum = ( myRS.getInt( "tablenumber" ));
                              subT = ( myRS.getDouble( "subtotal" ));

                              // throws null pointer exception
                              waiterNameJTextField.setText( waiter );
                  }

                  myRS.close();

            }

            catch( SQLException sqe )
            {
                  sqe.printStackTrace();
            }


   } // end method tableNumberJComboBoxItemStateChanged
0
Comment
Question by:shanemcf
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  • 4
10 Comments
 
LVL 92

Expert Comment

by:objects
ID: 10924890
check if waiterNameJTextField is null
maybe also check waiter
0
 

Author Comment

by:shanemcf
ID: 10924936
waiterNameJTextField not exclusively set to NULL,
 shouldn't var waiter contain the waitername from the dbase query?
 
 does my SQL statement look as if it is matching (int)tablenumber (from dbase)  to (int)tablenumber(from JComboBox) ?

not sure how to implement, or for that matter is it necessary to:

if( event.getStateChange() == ItemEvent.SELECTED ) ..............

If so, how so, or as I see it, ItemEvent.SELECTED seems to be the same, however, NOT working.

Oh yeah, I get duplicates when I System.out.println() it.
0
 
LVL 92

Expert Comment

by:objects
ID: 10924944
can u post the stack trace for the npe
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Author Comment

by:shanemcf
ID: 10924996
//////////////////  Line 534  ///////////////////////
Line 534 contains: waiterNameJTextField.setText( waiter );

Exception in thread "main" java.lang.NullPointerException
        at RestaurantBillCalculator.tableNumberJComboBoxItemStateChanged(Restaur
antBillCalculator.java:534)
        at RestaurantBillCalculator.access$400(RestaurantBillCalculator.java:10)

        at RestaurantBillCalculator$5.itemStateChanged(RestaurantBillCalculator.
java:296)
        at javax.swing.JComboBox.fireItemStateChanged(JComboBox.java:1161)
        at javax.swing.JComboBox.selectedItemChanged(JComboBox.java:1218)
        at javax.swing.JComboBox.contentsChanged(JComboBox.java:1265)
        at javax.swing.AbstractListModel.fireContentsChanged(AbstractListModel.j
ava:100)
        at javax.swing.DefaultComboBoxModel.setSelectedItem(DefaultComboBoxModel
.java:88)
        at javax.swing.DefaultComboBoxModel.addElement(DefaultComboBoxModel.java
:126)
        at javax.swing.JComboBox.addItem(JComboBox.java:690)
        at RestaurantBillCalculator.createWaiterJPanel(RestaurantBillCalculator.
java:304)
        at RestaurantBillCalculator.createUserInterface(RestaurantBillCalculator
.java:126)
        at RestaurantBillCalculator.<init>(RestaurantBillCalculator.java:104)
        at RestaurantBillCalculator.main(RestaurantBillCalculator.java:741)
Press any key to continue . . .
0
 
LVL 92

Expert Comment

by:objects
ID: 10925025
Then it looks like waiterNameJTextField is null.
0
 

Author Comment

by:shanemcf
ID: 10925087
I figured it out....

I was trying to use ItemEvent meths but trying to hard, teaches you to keep it simple.....

 Thanks Objects for your replies
////////////// Modified Code  ///////////////////////

try
            {
                  //select all columns from restaurantTable table
                  myRS=mySt.executeQuery( "select * from restauranttables " +
                  "where tablenumber = " + tableNumberJComboBox.getSelectedIndex() );


                  while( myRS.next() )
                  {
                              //match waiter name to table number
                              waiter = ( myRS.getString ( "waitername" ));
                              tableNum = ( myRS.getInt( "tablenumber" ));
                              subT = ( myRS.getDouble( "subtotal" ));

                              // throws null pointer exception
                              waiterNameJTextField.setText( waiter );
                  }

                  myRS.close();

            }
0
 
LVL 92

Expert Comment

by:objects
ID: 10925094
no worries :)
0
 

Author Comment

by:shanemcf
ID: 10925166
obj, how do these points systems work, and how should it work in this case?
0
 
LVL 92

Expert Comment

by:objects
ID: 10925337
up to u. u can ask CS for a refund or accept one of my comments as an answer
0
 
LVL 1

Accepted Solution

by:
Computer101 earned 0 total points
ID: 11187298
PAQed, with points refunded (50)

Computer101
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