Relation to java development to BPM

Hi friend ,
I am new to BPM ( bonita ) , I have one simple question business process management development and it's relation to java development.

For Example : After developing one business process , then what does the java developer does , how to they integrate in the java development , my expectation with java development refers to the generated Jar from bpm tools and move forward in java development by using the inheritance and passing the parameters to the methods like API ?..