I am sure you have an EBS instance to start with ,
If you have I suggest you to start with the tutorial guide which will come with the Jdeveloper folder you download.
Check the Note Note 416708.1 - How to find the correct version of JDeveloper to use with eBusiness Suite 11i or Release 12.x
to download the right Jdev.
And you can search in this forum itself there will be many link for start learning OAF.
To start with oaf definitely we require Core Java, Design Pattern knowledge then we should jump into tutorial tool box practise exercises.
I already have the knowledge of Core Java and MVC Architecture. Now i need to install Jdeveloper in my local system.
Since you 're from java back ground you can kick start oaf , please make sure that its very essential to download the exact version of
Jdeveloper which is compatible to your Oracle EBS and have Jevelopers guide for reference .