title: Java exception when trying to show Array
body: <p>So I'm trying to create an array list that stores the shape type, size and color. Then I want it to output in the terminal. Here's what I have, but I keep getting exceptions:</p>
  
  <pre><code>if (e.getSource() == storeData) {
        ShapeItem.add(shapeChoice.getSelectedItem()); //Add shape type
        ShapeItem.add(ShapeSize); //Add shape size
        ShapeItem.add(shapeColor); //Add shape color
  }
  
  else if (e.getSource() == showData) {
      while (it.hasNext()) {
          System.out.println(it.next());
      }
  }
  </code></pre>
  
  <p>And the declarations:</p>
  
  <pre><code>ArrayList ShapeItem = new ArrayList(); //Generic ArrayList to Store objects
  Iterator it = ShapeItem.iterator(); //Iterator to go through the array
  </code></pre>
  
  <p>It seems it should work, but here's what happens:
  (Sorry for the huge wall of text, but I have no idea what's important in exceptions)</p>
  
  <pre><code>Exception in thread "AWT-EventQueue-0" java.util.ConcurrentModificationException
      at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:819)
      at java.util.ArrayList$Itr.next(ArrayList.java:791)
      at Main.actionPerformed(Main.java:140)
      at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018)
      at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2341)
      at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
      at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
      at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
      at java.awt.Component.processMouseEvent(Component.java:6505)
      at javax.swing.JComponent.processMouseEvent(JComponent.java:3321)
      at java.awt.Component.processEvent(Component.java:6270)
      at java.awt.Container.processEvent(Container.java:2229)
      at java.awt.Component.dispatchEventImpl(Component.java:4861)
      at java.awt.Container.dispatchEventImpl(Container.java:2287)
      at java.awt.Component.dispatchEvent(Component.java:4687)
      at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832)
      at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4492)
      at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422)
      at java.awt.Container.dispatchEventImpl(Container.java:2273)
      at java.awt.Window.dispatchEventImpl(Window.java:2719)
      at java.awt.Component.dispatchEvent(Component.java:4687)
      at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:723)
      at java.awt.EventQueue.access$200(EventQueue.java:103)
      at java.awt.EventQueue$3.run(EventQueue.java:682)
      at java.awt.EventQueue$3.run(EventQueue.java:680)
      at java.security.AccessController.doPrivileged(Native Method)
      at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
      at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
      at java.awt.EventQueue$4.run(EventQueue.java:696)
      at java.awt.EventQueue$4.run(EventQueue.java:694)
      at java.security.AccessController.doPrivileged(Native Method)
      at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
      at java.awt.EventQueue.dispatchEvent(EventQueue.java:693)
      at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:244)
      at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:163)
      at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:151)
      at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:147)
      at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:139)
      at java.awt.EventDispatchThread.run(EventDispatchThread.java:97)
  Exception in thread "AWT-EventQueue-0" java.util.ConcurrentModificationException
      at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:819)
      at java.util.ArrayList$Itr.next(ArrayList.java:791)
      at Main.actionPerformed(Main.java:140)
      at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018)
      at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2341)
      at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
      at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
      at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
      at java.awt.Component.processMouseEvent(Component.java:6505)
      at javax.swing.JComponent.processMouseEvent(JComponent.java:3321)
      at java.awt.Component.processEvent(Component.java:6270)
      at java.awt.Container.processEvent(Container.java:2229)
      at java.awt.Component.dispatchEventImpl(Component.java:4861)
      at java.awt.Container.dispatchEventImpl(Container.java:2287)
      at java.awt.Component.dispatchEvent(Component.java:4687)
      at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832)
      at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4492)
      at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422)
      at java.awt.Container.dispatchEventImpl(Container.java:2273)
      at java.awt.Window.dispatchEventImpl(Window.java:2719)
      at java.awt.Component.dispatchEvent(Component.java:4687)
      at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:723)
      at java.awt.EventQueue.access$200(EventQueue.java:103)
      at java.awt.EventQueue$3.run(EventQueue.java:682)
      at java.awt.EventQueue$3.run(EventQueue.java:680)
      at java.security.AccessController.doPrivileged(Native Method)
      at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
      at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
      at java.awt.EventQueue$4.run(EventQueue.java:696)
      at java.awt.EventQueue$4.run(EventQueue.java:694)
      at java.security.AccessController.doPrivileged(Native Method)
      at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
      at java.awt.EventQueue.dispatchEvent(EventQueue.java:693)
      at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:244)
      at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:163)
      at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:151)
      at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:147)
      at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:139)
      at java.awt.EventDispatchThread.run(EventDispatchThread.java:97)
  Exception in thread "AWT-EventQueue-0" java.util.ConcurrentModificationException
      at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:819)
      at java.util.ArrayList$Itr.next(ArrayList.java:791)
      at Main.actionPerformed(Main.java:140)
      at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018)
      at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2341)
      at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
      at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
      at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
      at java.awt.Component.processMouseEvent(Component.java:6505)
      at javax.swing.JComponent.processMouseEvent(JComponent.java:3321)
      at java.awt.Component.processEvent(Component.java:6270)
      at java.awt.Container.processEvent(Container.java:2229)
      at java.awt.Component.dispatchEventImpl(Component.java:4861)
      at java.awt.Container.dispatchEventImpl(Container.java:2287)
      at java.awt.Component.dispatchEvent(Component.java:4687)
      at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832)
      at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4492)
      at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422)
      at java.awt.Container.dispatchEventImpl(Container.java:2273)
      at java.awt.Window.dispatchEventImpl(Window.java:2719)
      at java.awt.Component.dispatchEvent(Component.java:4687)
      at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:723)
      at java.awt.EventQueue.access$200(EventQueue.java:103)
      at java.awt.EventQueue$3.run(EventQueue.java:682)
      at java.awt.EventQueue$3.run(EventQueue.java:680)
      at java.security.AccessController.doPrivileged(Native Method)
      at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
      at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
      at java.awt.EventQueue$4.run(EventQueue.java:696)
      at java.awt.EventQueue$4.run(EventQueue.java:694)
      at java.security.AccessController.doPrivileged(Native Method)
      at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
      at java.awt.EventQueue.dispatchEvent(EventQueue.java:693)
      at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:244)
      at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:163)
      at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:151)
      at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:147)
      at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:139)
      at java.awt.EventDispatchThread.run(EventDispatchThread.java:97)
  Exception in thread "AWT-EventQueue-0" java.util.ConcurrentModificationException
      at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:819)
      at java.util.ArrayList$Itr.next(ArrayList.java:791)
      at Main.actionPerformed(Main.java:140)
      at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018)
      at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2341)
      at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
      at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
      at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
      at java.awt.Component.processMouseEvent(Component.java:6505)
      at javax.swing.JComponent.processMouseEvent(JComponent.java:3321)
      at java.awt.Component.processEvent(Component.java:6270)
      at java.awt.Container.processEvent(Container.java:2229)
      at java.awt.Component.dispatchEventImpl(Component.java:4861)
      at java.awt.Container.dispatchEventImpl(Container.java:2287)
      at java.awt.Component.dispatchEvent(Component.java:4687)
      at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832)
      at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4492)
      at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422)
      at java.awt.Container.dispatchEventImpl(Container.java:2273)
      at java.awt.Window.dispatchEventImpl(Window.java:2719)
      at java.awt.Component.dispatchEvent(Component.java:4687)
      at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:723)
      at java.awt.EventQueue.access$200(EventQueue.java:103)
      at java.awt.EventQueue$3.run(EventQueue.java:682)
      at java.awt.EventQueue$3.run(EventQueue.java:680)
      at java.security.AccessController.doPrivileged(Native Method)
      at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
      at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
      at java.awt.EventQueue$4.run(EventQueue.java:696)
      at java.awt.EventQueue$4.run(EventQueue.java:694)
      at java.security.AccessController.doPrivileged(Native Method)
      at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
      at java.awt.EventQueue.dispatchEvent(EventQueue.java:693)
      at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:244)
      at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:163)
      at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:151)
      at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:147)
      at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:139)
      at java.awt.EventDispatchThread.run(EventDispatchThread.java:97)
  </code></pre>