In a global economy, dealing with currencies, monetary amounts, conversions, rounding and formatting is complex. The new JavaMoney API was developed to meet these challenges. At the time of this writing, it was not yet incorporated into either Java SE or Java EE. You can read about JavaMoney at

https://java.net/projects/javamoney/pages/Home
http://jsr354.blogspot.ch

and you can obtain the software and documentation at

http://javamoney.github.io

Use JavaMoney to develop an application that will convert between two currencies specified by the user.