Replacing Hashtable With ConcurrentHashMap in Java
A ConcurrentHashMap can be replaced with Hashtable in Java.
But it requires careful observation, since locking behavior of Hashtable is different than that of ConcurrentHashmap.
A Hashtable locks whole Map instead of a portion of Map. Compound operations like if(Hashtable.get(key) == null) put(key, value) work in Hashtable but not in ConcurrentHashMap.
In a ConcurrentHashMap we use putIfAbsent() method for such a scenario