This is a 95% solution to the Scrooge Coin problem.
The other 5% is an extra credit excercise, which I probably will not do :)
The problem is the last task of the 1st week of the Bitcoin and Cryptocurrency Technologies by Princeton University - Coursera.
javac *.java
You can find a main class to test your solution here: https://gist.github.com/mentlsve/ef15013f1e6e5abd82996b34a7b4131b