[jboss-user] [EJB3] - ERROR [STDERR] java.lang.NullPointerException - can't solve

stefano bertozzi [http://community.jboss.org/people/bertoz84] created the discussion "ERROR [STDERR] java.lang.NullPointerException - can't solve" To view the discussion, visit: http://community.jboss.org/message/600753#600753 -------------------------------------------------------------- Hi all, i really need help to overcome this error. I'm going to paste the interesting parts of my code: *TEST BEAN ( we are inside a method called by the java test client ):* *     .* *     .* *     . *       try {                                         System.out.println("lowering the amount of the selected book");                                         Book abook = (Book) bookop.findByISBN(80002).get(0);  // Book is an entity bean --- bookop is the istance of a session bean that performs                                                                                                 // operations on Book *bookop.updateMin*(abook.getISBN(), 2); // tot - 2              // OPERATION updateMin *DONE* SUCCESSFULLY       } catch (Exception e) {                                         e.printStackTrace();       }       Users an_user = (Users) user.findByUser("mouse").get(0);  // Users is an entity bean --- user is the istance of a session bean that performs                                                                                                   // operations on Users *cart.checkoutCart*(an_user); // cart is the istance of a session statefull bean that performs classic operations like in a web site ( bookshop )                                                  // to see what this method go down -end *CART BEAN ( the called method ):* * *      public void *checkoutCart*(Users customer) {             for (int i = 0; i < books.size(); i++)   // where books is: private List<CartBook> books , a simple class made up of a Book and the quantity                                                                    // to purchase of that book                               {                                              Book abook = books.get(i).getBook();                                              Integer quantity = books.get(i).getQuantity();                  try {                          System.out.println("lowering the amount of the selected book"); *DBOperation.updateMin*(abook.getISBN(), quantity); // DBOperation is the same as bookop seen before                          // ERROR [STDERR] java.lang.NullPointerException                                              } catch (Exception e) {                          e.printStackTrace();                                              }                               }      } -end so basically the code is the same; the difference is that going through the cart bean i can lower the quantity of a list of books ( that are the books that a customer puts in his cart: when he performs a checkout operation the method updateMin lowers the amount of every books purchased in the store ) instead of only one. the problem is that through the cart i get always the ERROR [STDERR] java.lang.NullPointerException in the *DBOperation.updateMin* methods that is exactly the same of *bookop.updateMin*. Every cicle of the for( ) command i get this error. I can assure that my list is not empty and abook & quantity are not null. I really don't get the problem! Thank you in advance!! -------------------------------------------------------------- Reply to this message by going to Community [http://community.jboss.org/message/600753#600753] Start a new discussion in EJB3 at Community [http://community.jboss.org/choose-container!input.jspa?contentType=1&...]