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At startup, the GUI does not show up. Instead, I get an "Exception window", with the following backtrace: java.util.ConcurrentModificationException at java.util.AbstractList$Itr.checkForComodification(AbstractList.java:449) at java.util.AbstractList$Itr.next(AbstractList.java:420) at org.netbeans.modules.javacore.jmiimpl.javamodel.LightAttrList$LightAttrListIterator.next(LightAttrList.java:444) at org.netbeans.modules.javacore.jmiimpl.javamodel.FeaturesList$FeatureListIterator.next(FeaturesList.java:465) at org.netbeans.modules.java.bridge.ObjectsCollection.getElements(ObjectsCollection.java:109) at org.netbeans.modules.java.bridge.MethodsCollection.getMethods(MethodsCollection.java:76) at org.netbeans.modules.java.bridge.ClassElementImpl.getMethods(ClassElementImpl.java:565) at org.openide.src.ClassElement.getMethods(ClassElement.java:485) at org.openide.src.ClassElement.hasMainMethod(ClassElement.java:802) at org.netbeans.modules.jemmysupport.runinternally.RunInternallyAction.getSelectedMainClass(RunInternallyAction.java:204) at org.netbeans.modules.jemmysupport.runinternally.RunInternallyAction.enable(RunInternallyAction.java:98) at org.openide.util.actions.NodeAction.isEnabled(NodeAction.java:170) at org.openide.awt.Actions$ButtonBridge.updateState(Actions.java:674) at org.openide.awt.Actions$Bridge.addNotify(Actions.java:458) at org.openide.awt.Actions$Bridge$VisL.propertyChange(Actions.java:496) at java.beans.PropertyChangeSupport.firePropertyChange(PropertyChangeSupport.java:333) at java.beans.PropertyChangeSupport.firePropertyChange(PropertyChangeSupport.java:270) at java.awt.Component.firePropertyChange(Component.java:7159) at javax.swing.JComponent.addNotify(JComponent.java:4470) at java.awt.Container.addNotify(Container.java:2500) at javax.swing.JComponent.addNotify(JComponent.java:4469) at org.openide.awt.Toolbar.addNotify(Toolbar.java:568) at java.awt.Container.addNotify(Container.java:2500) at javax.swing.JComponent.addNotify(JComponent.java:4469) at java.awt.Container.addNotify(Container.java:2500) at javax.swing.JComponent.addNotify(JComponent.java:4469) at java.awt.Container.addNotify(Container.java:2500) at javax.swing.JComponent.addNotify(JComponent.java:4469) at java.awt.Container.addNotify(Container.java:2500) at javax.swing.JComponent.addNotify(JComponent.java:4469) at java.awt.Container.addNotify(Container.java:2500) at javax.swing.JComponent.addNotify(JComponent.java:4469) at javax.swing.JRootPane.addNotify(JRootPane.java:680) at java.awt.Container.addNotify(Container.java:2500) at java.awt.Window.addNotify(Window.java:466) at java.awt.Frame.addNotify(Frame.java:501) at java.awt.Window.show(Window.java:513) at java.awt.Component.show(Component.java:1300) at java.awt.Component.setVisible(Component.java:1253) at org.netbeans.core.windows.view.ui.MainWindow.setVisible(MainWindow.java:544) at org.netbeans.core.windows.view.DefaultView.showWindowSystem(DefaultView.java:526) at org.netbeans.core.windows.view.DefaultView.windowSystemVisibilityChanged(DefaultView.java:479) at org.netbeans.core.windows.view.DefaultView.changeGUI(DefaultView.java:163) at org.netbeans.core.windows.ViewRequestor.dispatchRequest(ViewRequestor.java:238) at org.netbeans.core.windows.ViewRequestor.processVisibilityRequest(ViewRequestor.java:227) at org.netbeans.core.windows.ViewRequestor.postVisibilityRequest(ViewRequestor.java:164) at org.netbeans.core.windows.ViewRequestor.scheduleRequest(ViewRequestor.java:85) at org.netbeans.core.windows.Central.setVisible(Central.java:74) at org.netbeans.core.windows.WindowManagerImpl.setVisible(WindowManagerImpl.java:710) at org.netbeans.core.windows.WindowSystemImpl.show(WindowSystemImpl.java:56) [catch] at org.netbeans.core.NonGui$3.run(NonGui.java:223) at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209) at java.awt.EventQueue.dispatchEvent(EventQueue.java:461) at java.awt.EventDispatchThread.pumpOneEventForHierarchy(EventDispatchThread.java:242) at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:163) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:157) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:149) at java.awt.EventDispatchThread.run(EventDispatchThread.java:110) I see two possible ways how my default project might be different from most other projects: 1) It uses a lot of generics. 2) I use subversion, and develop the code on two different computers. I notice that the files U nbproject/nbproject/project.xml U nbproject/nbproject/genfiles.properties are different on the two different computers, and every time I check in a version from the other computer, I see that those files are changed. I don't know if this might result in the problem?
The second time I try to start up netbeans, the exception does not occur. It seems to be some kind of thread-race bug.
*** This issue has been marked as a duplicate of 57272 ***
Reorganization of java component