Difference between Hashtable and Collections.synchronizedMap(HashMap)

Question

As far as I know, java.util.Hashtable synchronizes each and every method in the java.util.Map interface, while Collections.synchronizedMap(hash_map) returns a wrapper object

Answer 1

Another point of difference to note is that HashTable does not allow null keys or values whereas HashMap allows one null key and any number of null values. Since synchronizedMap is wrapper over HashMap, its behavior with respect to null keys and values is same as HashMap.