Using Oracle as a database

I have created a windows application using swing and hibernate. I have use Oracle as the database. I don't think its an open source. Will i have any difficulty later on?
Also, any other things i need to keep in mind, before dispatching the application?

You can use Oracle Express Edition. While it is not open source, it can be freely used even for business, but it has some limitations. It would be useful if you want to learn Oracle or want to develop software for Oracle specifically.

If you're using any other edition without a proper licence, you may be violating a law. There might be some provisions to use Oracle for learning purposes, but I'm not very sure about it. XE can be definitely used for free by anyone.

Thanks for your reply Martin Vajsar. Yes, i am using Oracle Express Edition.