need to know how to build Box's Open API specification file(s)

Hi Team,

I need to know how to build java code using Open API Specification files that Box provides.
Given below is the link available at Box's site for the Open API Specification files: 
https://github.com/box/box-openapi/tree/master/v2.0

In this I found there are 4 files: 
authorization.openapi-v2.json,
token.openapi-v2.json ,
openapi-v2.json ,
upload.openapi-v2.json.

I have the following questions. Could you please answer them?

How to build java code from these 4 files using OAS to JAVA converter?
Are all these 4 files mandatory to be included to build java code OR can we build using a single file individually?
If I had chosen authorization to be included in my java code, what are all the files that needs to be included?

My thanks in advance.

Warm regards,
Raman Palikala.