Numberfield, where only numbers can be written

Its simple in JSF, but no so simple in vaadin 8… NumberField lets anything to write
ValueChangeEvent is only triggered when a the value is a number, but if i write a non numeric character, it wont be triggered again, until i delete all non numeric chars, so solutions like the last, arent work
Why its even possible to write non numeric in a component, called NUMBERField?