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ERROR [STDERR] java.lang.NullPointerException - can't solve
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created by <a href="http://community.jboss.org/people/bertoz84">stefano bertozzi</a> in <i>EJB3</i> - <a href="http://community.jboss.org/message/600753#600753">View the full discussion</a>
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<div class="jive-rendered-content"><p>Hi all, i really need help to overcome this error.</p><p>I'm going to paste the interesting parts of my code:</p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p><strong>TEST BEAN ( we are inside a method called by the java test client ):</strong></p><p><strong>     .</strong></p><p><strong>     .</strong></p><p><strong>     .<br/></strong></p><p>      try {</p><p>                                        System.out.println("lowering the amount of the selected book");</p><p>                                        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</p><p>            <strong> bookop.updateMin</strong>(abook.getISBN(), 2); // tot - 2</p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p>             // OPERATION updateMin <strong>DONE</strong> SUCCESSFULLY</p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p>      } catch (Exception e) {</p><p>                                        e.printStackTrace();</p><p>      }</p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p>      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</p><p>      <strong>cart.checkoutCart</strong>(an_user); // cart is the istance of a session statefull bean that performs classic operations like in a web site ( bookshop )</p><p>                                                 // to see what this method go down</p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p>-end</p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p><strong>CART BEAN ( the called method ):</strong></p><p><strong><br/></strong></p><p>     public void <strong>checkoutCart</strong>(Users customer) {</p><p>            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</p><p>                              {</p><p>                                             Book abook = books.get(i).getBook();</p><p>                                             Integer quantity = books.get(i).getQuantity();</p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p>                 try {</p><p>                         System.out.println("lowering the amount of the selected book");</p><p>                        <strong> DBOperation.updateMin</strong>(abook.getISBN(), quantity); // DBOperation is the same as bookop seen before</p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p>                         // ERROR [STDERR] java.lang.NullPointerException</p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p>                                             } catch (Exception e) {</p><p>                         e.printStackTrace();</p><p>                                             }</p><p>                              }</p><p>     }</p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p>-end</p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p>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.</p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p>the problem is that through the cart i get always the ERROR [STDERR] java.lang.NullPointerException in the <strong>DBOperation.updateMin </strong>methods that is exactly the same of <strong> bookop.updateMin</strong>.</p><p>Every cicle of the for( ) command i get this error.</p><p>I can assure that my list is not empty and abook & quantity are not null.</p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p>I really don't get the problem!</p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p>Thank you in advance!!</p></div>
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