^\d+$
or
^[1-9]\d*|0$
----
===== Negative Integer =====
^-[1-9]\d*|0$
or
^((-\d+)|(0+))$
----
===== Positive Integer, excluding 0 =====
^[1-9]\d*$
or
^([1-9][0-9]*){1,3}$
or
^\+?[1-9][0-9]*$
----
===== Negative Integer, excluding 0 =====
^-[1-9]\d*$
or
^\-[1-9][0-9]*$
----