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
super.doOperation(operation);
		}
		
		public void insertTextConverter(ITextConverter textConverter, int index) {
			throw new UnsupportedOperationException();
		}
		
		public void addTextConverter(ITextConverter textConverter) {
			if (fTextConverters == null) {
				fTextConverters= new ArrayList(1);
				fTextConverters.add(textConverter);
			} else if (!fTextConverters.contains(textConverter))
				fTextConverters.add(textConverter);
		}
		
		public void removeTextConverter(ITextConverter textConverter) {
			if (fTextConverters != null) {
				fTextConverters.remove(textConverter);
				if (fTextConverters.size() == 0)
					fTextConverters= null;
			}
		}
		
		/*
		 * @see TextViewer#customizeDocumentCommand(DocumentCommand)
		 */
		protected void customizeDocumentCommand(DocumentCommand command) {
			super.customizeDocumentCommand(command);
			if (fTextConverters != null) {