About Question enthuware.ocajp.i.v7.2.1375 :

[sivarama2794]

Hello Paul,
long z = _123_456L; is invalid because it starts with underscore right
identifier name can start with _ but the values of the variable should not start with _
is this same for int and other primitives
for eg int y = _23; is this legal r illegal

[admin]

What happened when you tried it out?

[sivarama2794]

Its saying can't resolve the symbol
Thank you my doubt is cleared.