If I need to implement an Application (say, Financial Accounting) in
Java, how should I design the Classes and Objects in the Application ?

Assume my FA System is restricted to the following simple scope :

I] DATA STRUCTURES (Tables in a DBMS or Files) :

1) Accounts Master
2) Accounts Transactions


II] PROGRAMS :

1. Journal Voucher Posting program
2. Daily Transactions Report


Further, in this regard :

1. How do I connect to a Database ?
2. How do I pass SQL Commands to the Database ?
3. How do I write reports ?