I raised a bug that I couldn't use TextField<Integer> and was directed to use NumberField (see http://extjs.com/forum/showthread.php?t=62660).
The java doc is incorrect - NumberField can not be parameterized with generics. It extends from TextField<Number> but does not have a generic constructor.
The full comiler error is:
The javadoc states:
The type NumberField is not generic; it cannot be parameterized with arguments <Integer>
When the correct code is:
NumberField<Integer> field = new NumberField<Integer>;
NumberField field = new NumberField();