Simple Transaction Database Implementation
The transaction database supports following operations:
SET - record a new data entry
GET - search of a data entry in database
UNSET - clear the record of a data entry
NUMEQUALTO - search the number of occurrence of certain value
END - exit the program
BEGIN - start a new transaction entry
ROLLBACK - discard current transaction and go back to previous one
COMMIT - close all pending transactions and make the changes permanently
Data Structure:
Current program uses two HashMaps, one for database record and one for occurrence tracking.