Button button = ...; button.setTooltipText("tooltip text");
If it’s only for the label inside of a button, not the rest of the button, you’d probably add the label as a Span inside the button.
And the public API you’re looking for is Tooltip.forComponent(somecomponent);
(I can’t imagine why you’d want that to be honest, but it’s certainly doable)
Out of curiosity, why do you want to do it like that?
I think this should work:
Span span = new Span("Label");
Button button = new Button();
button.getElement().appendChild(span.getElement());
yeah I would definitely not use Buttons as dashboard cards…
but if you must, this should do it:
Span sp = new Span();
Tooltip.forComponent(sp);
...
Button btn = new Button();
btn.getElement().appendChild(sp.getElement());