Concurrent modification exception. What is causing this?

Question

Here is my the pasrt of code causing the exception I have put a line comment ti indicate the line where it occurs. In addition I would like to know the cause of this eception as its a first for me.
Here is the full exception ....
Exception in thread "AWT-EventQueue-0" java.util.ConcurrentModificationException
        at java.util.AbstractList$Itr.checkForComodification(AbstractList.java:3
72)
        at java.util.AbstractList$Itr.next(AbstractList.java:343)
        at Contact.modifyExisting(Contact.java:432)
        at Phonebook1.actionPerformed(Phonebook1.java:236)
        at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:19
95)
        at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.jav
a:2318)
        at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel
.java:387)
        at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242
        at javax.swing.AbstractButton.doClick(AbstractButton.java:357)
        at javax.swing.plaf.basic.BasicRootPaneUI$Actions.actionPerformed(BasicR
ootPaneUI.java:191)
        at javax.swing.SwingUtilities.notifyAction(SwingUtilities.java:1636)
        at javax.swing.JComponent.processKeyBinding(JComponent.java:2849)
        at javax.swing.KeyboardManager.fireBinding(KeyboardManager.java:267)
        at javax.swing.KeyboardManager.fireKeyboardAction(KeyboardManager.java:2
16)
        at javax.swing.JComponent.processKeyBindingsForAllComponents(JComponent.
java:2926)
        at javax.swing.JComponent.processKeyBindings(JComponent.java:2918)
        at javax.swing.JComponent.processKeyEvent(JComponent.java:2812)
        at java.awt.Component.processEvent(Component.java:5815)
        at java.awt.Container.processEvent(Container.java:2058)
        at java.awt.Component.dispatchEventImpl(Component.java:4410)
        at java.awt.Container.dispatchEventImpl(Container.java:2116)
        at java.awt.Component.dispatchEvent(Component.java:4240)
        at java.awt.KeyboardFocusManager.redispatchEvent(KeyboardFocusManager.ja
va:1848)
        at java.awt.DefaultKeyboardFocusManager.dispatchKeyEvent(DefaultKeyboard
FocusManager.java:697)
        at java.awt.DefaultKeyboardFocusManager.preDispatchKeyEvent(DefaultKeybo
ardFocusManager.java:962)
        at java.awt.DefaultKeyboardFocusManager.typeAheadAssertions(DefaultKeybo
ardFocusManager.java:834)
        at java.awt.DefaultKeyboardFocusManager.dispatchEvent(DefaultKeyboardFoc
usManager.java:661)
        at java.awt.Component.dispatchEventImpl(Component.java:4282)
        at java.awt.Container.dispatchEventImpl(Container.java:2116)
        at java.awt.Window.dispatchEventImpl(Window.java:2429)
        at java.awt.Component.dispatchEvent(Component.java:4240)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThre
ad.java:273)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.
java:183)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThre
ad.java:173)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:168)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:160)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:121)and the code.......
if(modifiedWork.length()>0)
                         try
                              modifiedWorkNum = Integer.parseInt(modifiedWork);
                         } //////// THIS IS LINE 372
                         catch(Exception e)
                              JOptionPane.showMessageDialog(null,"You may only enter numbers for a valid phone number to try again press the modify nutton again.","Error",JOptionPane.ERROR_MESSAGE);
                              validModify = false;
                              return;
                    }Thanks in advance...

Answer 1

Would you mind looking at my modifyExisting method I apologise as it is long. I have icluded a line comment on line 432.
public void modifyExisting()
     {// Start of modifyExisting()
          int count = 0;
          int count1 = 0;
          int count2 = 0;
          int modifiedCellNum, modifiedWorkNum, modifiedHomeNum = 0;
          boolean validModify = true;
          boolean found = false;
          String currentHome = "";
          String currentWork = "";
          String currentCell = "";
          if(phoneList.size() > 0)
               String nameOfContactToEdit = JOptionPane.showInputDialog(null,"Please enter the name of the contact you wish to edit details for or press cancel to exit");
               if(nameOfContactToEdit == null)
                    finish();
               if(nameOfContactToEdit.trim().length()<= 0)
                    JOptionPane.showMessageDialog(null,"You have entered an invalid name. Please try again.","Error",JOptionPane.ERROR_MESSAGE);
                    modifyExisting();
                    validModify = false;
                    return;
               String surnameOfContactToEdit = JOptionPane.showInputDialog(null,"Please enter the the surname for "+nameOfContactToEdit+" if one exists or press cancel to exit.");
               if(surnameOfContactToEdit == null)
                    finish();
               for(Person m: phoneList)
                    m = phoneList.get(count);
                    if((m.name).equals(nameOfContactToEdit.trim().toUpperCase())&&(m.surname).equals(surnameOfContactToEdit.trim().toUpperCase()))
                         currentHome = m.home;
                         currentWork = m.work;
                         currentCell = m.cell;
                         found = true;
                    count ++;
               if(found == true)
                    String modifiedName = JOptionPane.showInputDialog("Please enter the new name for contact or press cancel to keep it as "+nameOfContactToEdit+".");
                    if(modifiedName == null)
                         modifiedName = nameOfContactToEdit;
                    if(modifiedName.trim().length()<= 0)
                         JOptionPane.showMessageDialog(null,"You have entered an invalid name. Please press the modify button to try again.","Error",JOptionPane.ERROR_MESSAGE);
                         return;
                    if(modifiedName.trim().length()>10)
                         JOptionPane.showMessageDialog(null,"You may not enter a new name longer than 10 characters long. Please try again.","Error",JOptionPane.ERROR_MESSAGE);
                         validModify = false;
                         modifyExisting();
                         return;
                    String modifiedSurname = JOptionPane.showInputDialog("Please enter the new surname for contact or press cancel to keep it as "+surnameOfContactToEdit+".");
                    if(modifiedSurname == null)
                         modifiedSurname = surnameOfContactToEdit;
                    if(modifiedSurname.trim().length()>10)
                         JOptionPane.showMessageDialog(null,"You may not enter a surname longer than 10 characters long. Please try again.","Error",JOptionPane.ERROR_MESSAGE);
                         validModify = false;
                         modifyExisting();
                         return;
                    String modifiedHome = JOptionPane.showInputDialog("Please enter a new home number for "+modifiedName+" or press cancel to keep it as is.");
                    if(modifiedHome == null)
                         modifiedHome = currentHome;
                    if(modifiedHome.length()>0)
                         try
                              modifiedHomeNum = Integer.parseInt(modifiedHome);
                         catch(Exception e)
                              JOptionPane.showMessageDialog(null,"You may only enter numbers for a valid phone number to try again press the modify nutton again.","Error",JOptionPane.ERROR_MESSAGE);
                              validModify = false;
                              return;
                    if(modifiedHome.length() > 10)
                         JOptionPane.showMessageDialog(null,"You may not enter a number longer than 10 characters long. Please press the modify button to try again.","Error",JOptionPane.ERROR_MESSAGE);
                         validModify = false;
                         return;
                    String modifiedWork = JOptionPane.showInputDialog("Please enter a new home number for "+modifiedName+" or press cancel to keep it as is.");
                    if(modifiedHome == null)
                         modifiedWork = currentWork;
                    if(modifiedWork.length()>0)
                         try
                              modifiedWorkNum = Integer.parseInt(modifiedWork);
                         catch(Exception e)
                              JOptionPane.showMessageDialog(null,"You may only enter numbers for a valid phone number to try again press the modify nutton again.","Error",JOptionPane.ERROR_MESSAGE);
                              validModify = false;
                              return;
                    if(modifiedWork.length() > 10)
                         JOptionPane.showMessageDialog(null,"You may not enter a number longer than 10 characters long. Please press the modify button to try again.","Error",JOptionPane.ERROR_MESSAGE);
                         validModify = false;
                         return;
                    String modifiedCell = JOptionPane.showInputDialog("Please enter a new home number for "+modifiedName+" or press cancel to keep it as is.");
                    if(modifiedCell == null)
                         modifiedCell = currentCell;
                    if(modifiedCell.length()>0)
                         try
                              modifiedCellNum = Integer.parseInt(modifiedCell);
                         catch(Exception e)
                              JOptionPane.showMessageDialog(null,"You may only enter numbers for a valid phone number to try again press the modify nutton again.","Error",JOptionPane.ERROR_MESSAGE);
                              validModify = false;
                              return;
                    if(modifiedCell.length() > 10)
                         JOptionPane.showMessageDialog(null,"You may not enter a number longer than 10 characters long. Please press the modify button to try again.","Error",JOptionPane.ERROR_MESSAGE);
                         validModify = false;
                         return;
                    if((modifiedHome.length() <= 0) && (modifiedWork.length() <= 0) && (modifiedCell.length() <= 0))
                         JOptionPane.showMessageDialog(null,"The contact must have at least one number to be included in the phonebook. Please press modify button to try again.","Error",JOptionPane.ERROR_MESSAGE);
                         validModify = false;
                         return;
                    for(Person z: phoneList)
                         z = phoneList.get(count1);
                         if((z.name).equals(modifiedName.trim().toUpperCase()) && (z.surname).equals(modifiedSurname.trim().toUpperCase()))
                              JOptionPane.showMessageDialog(null,"You may not enter duplicate contacts. Please try again.","Error",JOptionPane.ERROR_MESSAGE);
                              validModify = false;
                              modifyExisting();
                              return;
                         count1 ++;
                    if(validModify == true)
                         for(Person contactToMod: phoneList)/////////////////////////////////////////////////////// line 432
                              contactToMod = phoneList.get(count2);
                              if((contactToMod.name.equals(nameOfContactToEdit.trim().toUpperCase())) && (contactToMod.surname.equals(surnameOfContactToEdit.trim().toUpperCase())))
                                   try
                                        contactToMod.setName(modifiedName.trim().toUpperCase());
                                        contactToMod.setSurname(modifiedSurname.trim().toUpperCase());
                                        contactToMod.setHome(modifiedHome);
                                        contactToMod.setWork(modifiedWork);
                                        contactToMod.setCell(modifiedCell);
                                        phoneList.add(contactToMod);
                                        JOptionPane.showMessageDialog(null,"Updated contact succesfully.","Information",JOptionPane.INFORMATION_MESSAGE);
                                   catch(Exception e)
                                        JOptionPane.showMessageDialog(null,"The contact was not updated. If probelm persists please contact system administrator.","Error",JOptionPane.ERROR_MESSAGE);
                              count2 ++;
               else
                    JOptionPane.showMessageDialog(null,"No contact with that name and surname exists. Please press the modify button to try again.","Error",JOptionPane.ERROR_MESSAGE);
          else
               JOptionPane.showMessageDialog(null,"The phone list is empty and there are no contacts to modify.","Information Message",JOptionPane.INFORMATION_MESSAGE);
     }// End of modifyExisting()Edited by: Yucca on May 6, 2008 8:12 PM