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
/*
	 * @see JavaEditor#synchronizeOutlinePageSelection()
	 */
	public void synchronizeOutlinePageSelection() {
		
		if (isEditingScriptRunning())
			return;
		
		ISourceViewer sourceViewer= getSourceViewer();
		if (sourceViewer == null || fOutlinePage == null)
			return;
			
		StyledText styledText= sourceViewer.getTextWidget();
		if (styledText == null)
			return;
		
		int offset= sourceViewer.getVisibleRegion().getOffset();
		int caret= offset + styledText.getCaretOffset();
		
		IJavaElement element= getElementAt(caret, false);
		ISourceReference reference= getSourceReference(element, caret);
		if (reference != null)
			fOutlinePage.select(reference);
	}
	
	private ISourceReference getSourceReference(IJavaElement element, int offset) {
		
		if ( !(element instanceof ISourceReference))
			return null;