Remove commented out code.
Remove dead code.  Use ConcurrentHashMap.
Synchronise _sortChangeListeners list.
Use ArrayList instead of LinkedList.
Use ArrayList not LinkedList.
Sync changeListeners.  Use ArrayList.
Tidy collection sync.
Sonar fixes.
Redundant modifiers.
Constants class should be interface.
Modifier order.
Sonar: Loose coupling.
Make helper classes final.
redundant modifier.
Modifier order.
Remove redundant calls to Math.floor
comment
use entrySet()
fix validation
fix synchronized