To expertise java programming?

[Siseneg]

A forum depends very heavily on the database structure. You want to nail that first. You don't need Java for that.

OP wanted to increase their Java programming skills and in no way mentioned creating a forum.

Could you please enlighten me to the relevance of your post?

[Siseneg]

A forum depends very heavily on the database structure. You want to nail that first. You don't need Java for that.
Posts and replies
Posts with parents and children
Forums
Subforums
Users
Permissions
Achievements
Ratings
(temporarily) banning on username/ip
Logging
Maintenance mode
Pruning
The list goes on and on.
Create a backend that will pull the data. EJB's that use plain old DAO's, Hibernate, any other ORM, or just plain JPA.
A webservice that serves it to the frontend (Possibly usng JSON for your asynchronous client).
A HTML client using React, Ember2, or Angular2.
SASS for creating CSS


This will keep you busy for a day or two

One more in a long line of posts you plagiarized from another source and posted here as your own. This one is from a 07-27-20*6 post by someone named Arel on the techonce.net forums:

http://www.techonce.net/threads/*2078*0-Re-What-do-I-need-to-learn-to-write-Java-forum-software

[kaufen]

You can find the materials to learning the java in everything from online tutorials to books such as 'java programming for dummies. You might also want to do some background reading on Object-Oriented programming, but most books/tutorials will point these out for you. i s***est doing a simple google search on java programming tutorials.