| HashMap | Hashtable |
| Every method in HashMap is not synchronized | Every method in Hashtable is Synchronized |
| No thread Safe | Thread Safe |
| Relatively performance is high | Relatively performance is low |
| Null key and Null values allowed in HashMap | Null key and Null value not allowed in Hashtable |
| Not legacy class, introduced in java 1.2 | Legacy class, introduced in java 1.0 |
| We can get synchronized version of HashMap by passing it to Collection.synchronizedMap() method | No such functionality to disable chronization is available here. |