| ConcurrentHashMap | syncronizedMap() | Hashtable |
| Thread safety without locking the complete map | Thread safety by locking the complete map | Thread safety by locking the complete map |
| At a time multiple Threads are allowed to operate on map in safe manner | At a time one single Thread is allowed to operate in safe manner | At a time one single Thread is allowed to operate in safe manner |
| Write operation requires segment/bucket level locks | Every read and write operations requires total map lock | Every read and write operations requires total map lock |
| While iterating if modified we will not get ConcurrentModificationException | While iterating if modified we will get ConcurrentModificationException | While iterating if modified we will get ConcurrentModificationException |
| Iterator is fail fast | Iterator is fail safe | Iterator is fail safe |
| Null not allowed for both keys are values | Null allowed for both keys and values | Null not allowed for both keys are values |
| Introduced in v1.5 | Introduced in v1.2 | Introduced in v1.0 v(Legacy Class) |
