true/false in expression

Sometimes having boolean true/false in an expression are needed. See discussion:

Example from Øyvind Harboe:
Expression e=ExpressionFactory.expTrue();
if (xxx)
{
e=e.andExp(....);
}
if (yyy)
{
e=e.andExp(....);
}
return e;

http://mail-archives.apache.org/mod_mbox/incubator-cayenne-user/200608.mbox/%3cAB568C55-2716-4F5A-B498-1F0CBDC71BE6@objectstyle.org%3e

http://mail-archives.apache.org/mod_mbox/incubator-cayenne-user/200608.mbox/%3cc09652430608161347ka3eac59y3803eb1c80322f13@mail.gmail.com%3e