use double, big decimal and int to do money calculation
[use function objects] simple version
[use function objects] use static final to hold the instance
[use function objects] rename the instance name to upper case and instance
[use function objects] add interface for comparator
[use function objects] add host class and make the compare no access
[favor generic type] initial codes
[favor generic type] eliminate obsolete reference
[favor generic type] add generic type
[favor generic type] use type cast, which causes a warning
[favor generic type] add suppress warning