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HashMap and Hashtable are data structures in Java that associate keys with values. The two data structures are so similar to one another that, in some applications, leveraging either implementation would not make a difference.
Even though HashMap and Hashtable are relatively similar, it is still vital to know when to use them because using them wrongly could have unfavorable effects. In this article, get an in-depth Hashmap Vs Hashtable comparison, and learn what makes them unique from one another. In this guide we will first see the difference between HashMap and Hashtable based on a few important factors and then we will see what is Hashtable and HashMap.
Here, we will see the difference between HashMap and Hashtable based on a few important factors:
Basis | Hashmap | Hashtable |
---|---|---|
Definition | Hashmap, a type of nap implementation, leverages hashtable for storage. | It is a Legacy Map deployment that, too, leverages Hashtable for storage. |
Thread Safety | No | Yes |
Null Keys | Permitted | Not Permitted |
Use Cases | Map Implementation for General Purpose | Legacy Map Implementation and Thread safe |
Performance | Faster Than Hashtable | Slower Than Hashmap |
Null Values | Permitted | Not Permitted |
Iterator | Fail Fast | Not Fail Fast |
Inheritance | Extends AbstractMap | Extends Dictionary |
Here is a proper illustration of Hashmap Vs Hashtable at work for your better understanding:
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Let’s deep dive into the difference between HashMap and Hashtable based on a usage and recommendations.
Java supports both HashMap and Hashtable as key-value data structures. Hash tables are used in both cases, although there are some significant distinctions between them. Because HashMap isn’t synchronized, it’s not thread-safe. This means that multiple threads cannot safely access a HashMap simultaneously. However, since synchronization checks are unnecessary, HashMap is quicker than Hashtable.
Hashtable is thread-safe because it is synchronized. This indicates that concurrent access by several threads to a hashtable is not problematic. However, since synchronization checks are required, Hashtable is slower than HashMap.
Recommendations:
For Hashmap:
For Hashtable:
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Now we have seen the major difference between Hashmap and Hashtable. Now let’s move on to understand what is Hashmap and Hashtable individually.
HashMap is one of the Java collection classes. When it comes to Hashmap Vs Hashtable, the former implements the Map interface using a table-based extension of the AbstractMap class. HashMap is an unsynchronized data structure that supports many null values but only one null key object.
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In this Hashmap Vs Hashtable section, check out the key Hashmap functions.
Pros of Hashmap | Cons of Hashmap |
---|---|
Hashmap can look up items in an instance, thanks to their ability to map a key to a bucket in the hash table in seconds. | Collisions happen when two keys hash to the same bucket. It can considerably slow down the lookups and inserts. |
Due to the fact that just the keys and values—not the elements’ order—need to be stored, hashmaps can be extremely memory-efficient. | Since hashmaps don’t maintain the order of the items, they are inappropriate for applications where it matters. |
Hashmaps may be thread-safe, allowing many threads to access it concurrently without running into problems. | Implementing hashmaps can be difficult, particularly if you need to construct your own Hash algorithm. |
The HashTable class is widely used to create a hash table that links and associates keys with values. Non-null objects are acceptable here as both a key and a value. Remember that the objects you use as keys must support both the equals and hashCode methods to successfully store and retrieve objects from a hashtable.
In this Hashmap Vs Hashtable section, explore the various Hashtable functions:
Pros of Hashtable | Cons of Hashtable |
---|---|
It ensures perpetual time lookups. Values can typically be looked up using hash tables in a fixed amount of time. | Collisions, which happen when two separate keys hash to the same value, might affect hash tables. |
Since only the key and value of each item need to be stored, hash tables can be incredibly space-efficient. | Since hash tables aren’t properly ordered, it can be challenging to iterate through the elements in a particular sequence. |
A hash function and a collision avoidance method are the only tools to create hash tables. | Nil |
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