HashMap VS Hashtable In Java: In this article, we will discuss the difference between HashMap and Hashtable Java classes in detail i.e.; HashMap vs Hashtable
Hashtable is legacy class and based on hashcode of keys where keys are unique and it is exactly the same as HashMap with few differences with respect to following points
- Synchronized methods
- Performance
- Null key insertion
- Null value insertion
Lets us move on and discuss the key differences between these 2 Map implemented classes
HashMap vs Hashtable
HashMap |
Hashtable |
| HashMap is introduced in collection framework in Java 1.2 version | Hashtable is a legacy class and introduced in Java 1.0 version |
| HashMap is NOT synchronized | Hashtable is synchronized |
| All methods of HashMap is NOT synchronized i.e.; it is not thread-safe | All methods of HashMap is synchronized i.e.; thread-safe |
| Multiple threads are allowed to access | Only one thread is allowed access; other threads have to wait to get access, after obtaining lock/monitor |
| Performance-wise, this is relatively high comparing with Hashtable, as there is no wait time | Performance-wise, this is relatively slow due to synchronized methods as there is only one thread allowed to access, at any given point of time |
| NULL insertion allowed for both keys and values | NULL insertion is not allowed for both keys and values |
| Maximum of one NULL key and there is no upper limit for values | Simply, not allowed for both keys & values |
Note: both use the hash table data structure to store key-value pairs
When to use HashMap?
- HashMap stores key-value pairs which use a hashing technique to store key-value pairs where methods are NOT synchronized
- So, the search operation is faster with multiple threads access
- So, if the business requirement is to store key-value pairs for faster search operation or number of search operation on the basis of keys; without concerning concurrent access to the map
- Then, HashMap is the very apt choice
When to use Java Hashtable?
- This is exactly the same as that of HashMap, but every method is synchronized
- Performance-wise is relatively slower than comparing HashMap
- So, if the business requirement is to store key-value pairs for faster search operation with synchronized access
- Then, Java Hashtable is the preferred choice over HashMap
