Oracle Express Edition (XE) is "an entry-level, small-footprint database based on the Oracle Database 11g Release 2 code base. It's free to develop, deploy, and distribute; fast to download; and simple to administer".
This is a great option if you want to explore Oracle technology or build a prototype for an application that will be deployed on one of Oracle's enterprise databases. You can also use it to deploy your own small applications. However, XE is quite limited in how much data it can store (11GB), how many databases you can create (one) and how many CPUs it can use (one).
So you could use XE initially, then scale up to one of Oracle's commercial licences later on e.g. if your company already has access to Oracle DBA skills to support this. Alternatively you might prefer to go for an open source database like MySQL or (my preference) PostgreSQL, but you'll still need to think about how you are going to support and manage your database for a commercial application.
Kishor Joshi wrote:and same I want to know for Oracle database Products which is free and Which is not?
TBH, most of the databases mentioned will probably do you just fine - and there's also JavaDB, which was written specifically to integrate easily with Java programs and jars - so I would spend your effort in making sure that your app can work with any of them, with minimal effort.
Unfortunately, that's not necessarily a given, as SQL itself differs from db to db; but there are middleware tools around, like Hibernate, which simplifies the process of "database to POJO conversion" and offers its own query language which is the same across the board.
However, if you don't want to go that route, I think I might try an Oracle-based db, simply because Oracle now owns Java, so it's products are likely to be highly integrated. And, as chris said, it offers a path for deployment with a free version which you can then upgrade as and when your product does become "commercial".
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