Welcome to DBA world !!!

To learn Oracle Database Administration, you don't need to learn Java. First you need to understand the RDBMS concepts. Once you are good in concepts and start practicing you will get familiar with writing basic SQL statements which is good to start with.

You can download complete Oracle RDBMS documentation here for free. You can also download RDBMS software from here and Install in your laptop for free (education purpose only).

All the best.

Thanks,