Using already open window

I am newbie to selenium and trying to write a test script to for browser based application.

1) Login to app using user id and password.
2) Login to Database and required account no.
3) Search account no.

I have written 4 java classes.
a) LoginDo.java to open the browser with required URL.
b) ConnectDB.java to connect to DB to get correct account no.
c) AccountSearch.java to search the account in already open brower.
d) TakePayment.java calls above three in this sequence.

Is there anyway i can achieve this. Any help would be great.

I can post code of these classes if required.

thanks guys i got it sorted by the handler from main class to others.