Updated February 21, 2023
Difference between Hash Table vs Hash Map
Hash Table vs Hash Map will give out the differences of Hash Table and Hash Map. Both of these are used to store unique keys using hashing techniques. These are based on hashing and map implementation data structure. Hash Table implements associative array abstract type, a data structure that maps keys to values. It uses a hash function in computing an index, known as hash code, into an array of slots or buckets from where the desired value can be found. Let’s dig deeper into the Comparison of Hash Table vs Hash Map.
Head to Head Comparison between Hash Table vs Hash Map (Infographics)
Below are the top 13 differences between Hash Table vs Hash Map:
Key Differences between Hash Table vs Hash Map
Following are the key differences given below:
- Hash Table was introduced in Java’s first version, i.e. JDK 1.0, but it was refactored in JDK 1.2 for implementing the Map interface, making it a member of the Java Collections Framework.
- Hash Map was introduced in version 2 of Java JDK 1.2
- Hash Table is synchronized and hence has slower operations compared to Hash Map. If a user is not working in a multi-threaded environment, Java JDK recommends using Hash Map.
- Hash Table extends dictionary, i.e., it maps non-null keys to values. Users can look up the value that corresponds to keys.
- In Java, Hash Table and Hash Map use java util properties like java.util.Hashtable and java.util.HashMap respectively
- Hash Table and Hash Map don’t mention any insertion order in Java.
- Both Hash Map and Hash Table are implementations of java.util.Map interfaces in Java
- For Hash Map and Hash Table, Complexity offered by GET and PUT methods in worst and best case in O(n) and O(1), respectively.
- Synchronization operation will result in poor performance and hence avoided, and Hash Map is the one which is used.
- Methods like get(), put(), remove(), containsKey() provide constant time performance. Internally, these work based on the concept of hashing buckets for storing data
- Hash Map and Hash Table are resized when a number of elements reach the loadFactor. These are faster with smaller loadFactor and take up space. Hashing function works better with prime number capacity.
Comparison Table
Comparison between Hash Table vs Hash Map is given below:
|
Hash Table |
Hash Map |
| Hash table is the legacy class and was introduced before Hash map | On the other hand, Hash Map is the advanced version of Hash Table and was introduced as a new class in JDK1.2 |
| Hash Table is internally implemented in such a manner that no null key or null value is allowed | Whereas Hash Map allows one null key and multiple null values |
| Hash Table is synchronized and thread-safe, hence can be shared with other threads | There is no synchronization implemented in Hash Map, also not thread-safe. So it can not be shared among other threads without perfect synchronization code |
| Hash Table provides Iterator as well as Enumerator to traverse values stored in it | Hash Map provides an iterator for iteration/Traverse the values stored in it |
| In Hash Table, due to synchronization, hash table slows down compared to Hash map but also eliminates extra coding | As synchronization is absent, hash map is comparatively faster than hash table, preferable when there is no synchronization |
| Hash Table inherits dictionary class | Hash map inherits Abstract Map class |
| Hash Table does not maintain mappings in any particular order | Hash Map maintains insertion order and sorts mappings based on ascending key order |
| Hash Table is not a part of the collection framework. It was made part of collection framework member after implementing the Map interface | Hash Map implements a map interface and is part of a collection framework since the start |
| If there is a thread-safe operation to be used, Hash table can be used as all methods in it are synchronized | Hash Map is used for multi-threaded environment, recommended to use Concurrent Hash Map |
| Hash Table uses keys to implement hash code | Hash Map is an advanced improvement on Hash Table. |
| Hash Table Efficiency is O(1) | Hash Map Efficiency is O(1) |
| Enumerator in Hash Table is not a fail fast and throws ConcurrentModificationException | Iterator in Hash Map is fail fast iterator |
| Hash Table is preferred over Hash Map for multi-threaded applications. Oracle has
provided with ConcurrentHashMap as a replacement for Hash Table |
Hash Map is preferred over Hash Table for nonthreaded applications |
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This is a guide to Hash Table vs Hash Map. Here we also discuss the hash table vs hash map key differences with infographics and a comparison table. You may also have a look at the following articles to learn more –
