Bug 63155 [Refactoring] no user feedback when error during implicit refactoring triggered by drag'n'drop
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/packageview/SelectionTransferDropAdapter.java
private int handleValidateLink(Object target, DropTargetEvent event) {
		if (target instanceof IType && AddMethodStubAction.canActionBeAdded((IType)target, getSelection()))
			return DND.DROP_LINK;
		else		
			return DND.DROP_NONE;
	}
	
	private void handleDropMove(final Object target, DropTargetEvent event) throws JavaModelException, InvocationTargetException, InterruptedException{
		IJavaElement[] javaElements= ReorgUtils.getJavaElements(fElements);
		IResource[] resources= ReorgUtils.getResources(fElements);
		ReorgMoveStarter starter= null;
		if (target instanceof IResource) 
			starter= ReorgMoveStarter.create(javaElements, resources, (IResource)target);
		else if (target instanceof IJavaElement)
			starter= ReorgMoveStarter.create(javaElements, resources, (IJavaElement)target);
		if (starter != null)
			starter.run(getShell());
	}
	private int handleValidateCopy(Object target, DropTargetEvent event) throws JavaModelException{
		if (fCopyRefactoring2 == null) {
			IResource[] resources= ReorgUtils.getResources(fElements);
			IJavaElement[] javaElements= ReorgUtils.getJavaElements(fElements);
			fCopyRefactoring2= CopyRefactoring.create(resources, javaElements, JavaPreferencesSettings.getCodeGenerationSettings());
		}
		
		if (!canCopyElements())
			return DND.DROP_NONE;	
		if (target instanceof IResource && fCopyRefactoring2 != null && fCopyRefactoring2.setDestination((IResource)target).isOK())
			return DND.DROP_COPY;
		else if (target instanceof IJavaElement && fCopyRefactoring2 != null && fCopyRefactoring2.setDestination((IJavaElement)target).isOK())