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
private List fTextConverters;
		private OverviewRuler fOverviewRuler;
		private boolean fIsOverviewRulerVisible;
		
		private IVerticalRuler fCachedVerticalRuler;
		private boolean fCachedIsVerticalRulerVisible;
		
		
		public AdaptedSourceViewer(Composite parent, IVerticalRuler ruler, int styles) {
			super(parent, ruler, styles, CompilationUnitEditor.this);
			
			fCachedVerticalRuler= ruler;
			fCachedIsVerticalRulerVisible= (ruler != null);
			fOverviewRuler= new OverviewRuler(VERTICAL_RULER_WIDTH);