Bug 19075 Rename Java file to non Java file causes most actions to crash
F2 - open Java file in editor - rename it so that it has the extension .txt Almost all Java relevant actions in Edit, Source, Refactor, Naviagte and context menu are still enabled. Executing them almost always leads to some sort of exceptions.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/javaeditor/CompilationUnitEditor.java
if (p.isDeleted(getEditorInput())) {
			
			if (isSaveAsAllowed()) {
				
				/*
				 * 1GEUSSR: ITPUI:ALL - User should never loose changes made in the editors.
				 * Changed Behavior to make sure that if called inside a regular save (because
				 * of deletion of input element) there is a way to report back to the caller.
				 */
				 performSaveAs(progressMonitor);
			
			} else {
				
				/* 
				 * 1GF5YOX: ITPJUI:ALL - Save of delete file claims it's still there
				 * Missing resources.
				 */
				Shell shell= getSite().getShell();
				MessageDialog.openError(shell, JavaEditorMessages.getString("CompilationUnitEditor.error.saving.title1"), JavaEditorMessages.getString("CompilationUnitEditor.error.saving.message1")); 
			}
			
		} else {	
			
			setStatusLineErrorMessage(null);
			
			IWorkingCopyManager manager= JavaPlugin.getDefault().getWorkingCopyManager();
			ICompilationUnit unit= manager.getWorkingCopy(getEditorInput());
			
			if (unit != null) {
				synchronized (unit) {