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
* 
	 * @param event the property change event
	 */
	protected void handlePreferencePropertyChanged(org.eclipse.core.runtime.Preferences.PropertyChangeEvent event) {
		AdaptedSourceViewer asv= (AdaptedSourceViewer) getSourceViewer();
		if (asv != null) {
			String p= event.getProperty();					
			if (CODE_FORMATTER_TAB_SIZE.equals(p)) {
				asv.updateIndentationPrefixes();
				if (fTabConverter != null)
					fTabConverter.setNumberOfSpacesPerTab(getTabSize());
			}
		}
	}
	
	/*
	 * @see AbstractTextEditor#affectsTextPresentation(PropertyChangeEvent)
	 */
	protected boolean affectsTextPresentation(PropertyChangeEvent event) {
		String p= event.getProperty();
		boolean affects=MATCHING_BRACKETS_COLOR.equals(p) || CURRENT_LINE_COLOR.equals(p) || PROBLEM_INDICATION_COLOR.equals(p);
		return affects ? affects : super.affectsTextPresentation(event);
	}
	
	/*
	 * @see JavaEditor#createJavaSourceViewer(Composite, IVerticalRuler, int)
	 */
	protected ISourceViewer createJavaSourceViewer(Composite parent, IVerticalRuler ruler, int styles) {
		return new AdaptedSourceViewer(parent, ruler, styles);
	}