Nimish,
Whether or not the "=" operator is case sensitive is database specific. I think Oracle does not use case sensitivity here which is in line with what you are seeing. I can think of three things to try:
1) retrieve the password and compare in
java select password from usertable where username = 'user'
2) use the like operator - sometimes like is more strict
select * from usertable where password like "abcd"
3) use a PreparedStatement - the driver may give you case insensitivity
select * from usertable where password like ?
Personally, I prefer option one because it is less dependent on the database. It's also the only one I am positive will work.