HashMap vs Hashtable: Difference and Comparison

HashMap performs the basic map interface execution in Java. A Hashtable is executed from a Hashtable class that maps the key to values. Both HashMap and Hashtable are executed in the map interface in Java.

Hence, they are closely related to each other, yet they are immensely different from each other in many aspects.

Key Takeaways

1. HashMap allows null values and is not synchronized, while HashTable does not allow null values and is synchronized.
2. HashMap is faster than HashTable because it needs to be synchronized.
3. HashTable is thread-safe, while HashMap is not.

HashMap vs Hashtable

The difference between HashMap and Hashtable is that HashMap enables duplicate values for both keys and values, whereas, Hashtable does not enable any duplicate values for both keys and values. HashMap is not concurrent. Hence they enable multiple threads to approach them, whereas, Hashtable is concurrent and does not enable multiple threads to approach them.

Hashmap is a data structure that stores unique keys and values in Java. The HashMap class is well organized for positioning a value, inserting entries, and deleting entries.

Moreover, the entries found in HashMap are not ordered. The HashMap is not safe for threads as it enables multiple threads to approach them.

Hashtable keeps on track of declared variables in Java. Hashtable always depends upon the load factor rather than the number of items present in the table. Hence the execution of Hashtable is very slow.

The Hashtable is safe from multiple threads as it does not enable multiple threads to approach them.

Comparison Table

Parameters of comparison	HashMap	Hashtable
Concurrency	HashMap is not concurrent, hence they enable multiple threads approaching them that is they are not safe from multiple threads.	The Hashtable is concurrent and safe of multiple threads as it does not enable multiple threads to approach them.
Speed	The HashMap execution takes place at high speed.	The Hashtable execution takes place at a very slow speed.
Null value acceptance	HashMap accepts null values for both key and values.	Hashtable does not enable any null value for both keys and values.
Iterator	Iterator is fail-fast and sometimes throws ConcurrentModificationException.	The enumerator is not fail-fast and does not throw any ConcurrentModificationException.
Class Inheritance	AbstractMap class.	Dictionary class.
Application	HashMap is used in web pages, and web applications.	Hashtable is used for Online Spelling checkers and in-game programs.

What is HashMap?

HashMap is a collection of unique keys and values that performs the basic map interface execution in Java. The key can be found as indexes in the list, but in Map, it is found as an object.

Moreover, each key maps to only one value. The HashMap class has a systematic way of locating a value, inserting and deleting entries.

The HashMap has different types of constructors. HashMap() constructor is a type of constructor used to empty the HashMap with a default initial capacity and a default load factor.

A Hashmap contains duplicate values, and the entries found in HashMap are not ordered. For instance, the public class HashMap <K, V> extends AbstractMap<K, V implements Map<K, V>, cloneable, serializable.

HashMap( int initial capacity) is a type of constructor used to empty the HashMap with a specified initial capacity and a default load factor. Moreover, HashMap( int initial capacity, float load factor) constructor empties the HashMap with a specified initial capacity and a load factor.

HashMap is not concurrent. Hence they mostly enable multiple threads to approach them, and due to a well-organized behavior, execution is rapid.

HashMap(Map<? extends K, ? extends V>m) is used to build a new HashMap with the same previous mapping as the specified Map. HashMaps are used in Web pages and Web applications.

What is Hashtable? 

Hashtable is concurrent and is mostly executed from a Hashtable class that maps the key to values. Due to the concurrent nature of Hashtable, multiple threads do not face-approach them.

Hashtable is very simple to execute and has duplicate values. Moreover, it performs a basic map interface execution in Java.

In Hashtable, if the keys are found to be strings, the hash function converts them into numerical, but if the input key is found to be integers, then Key mod TableSize is used.

The hash function is easy to compute, yet hashtable execution takes place at a very slow speed. The low speed is due to the large size of the Hashtable, and it does not allocate the keys.

Hashtable is used to execute the insertion and to find specific operations in a constant average time. Hashtable mainly depends on the load factor rather than the number of items present in it.

In Hashtable, it is important to have a prime TableSize, the right choice of the load factor, and the hash function.

In Hashtable, a second hash function is also present, which is used for collision resolution. Hashtable is used in compilers to execute symbol tables, game programs such as transposition tables, and online spelling checkers.

Main Differences Between HashMap and Hashtable

1. HashMap is not concurrent. Hence they enable multiple threads to approach, whereas, Hashtable is concurrent and does not enable multiple threads to approach them.
2. The iterator is fail-fast and sometimes throws ConcurrentModificationException, whereas the enumerator is not fail-fast and does not throw any ConcurrentModificationException.
3. HashMap does not contain any duplicate values, whereas Hashtable contains duplicate values.
4. Hashmap is systematic and well-organized, whereas Hashtable is simple and not well-organized.
5. In Hashmap, the execution takes place at high speed, whereas in Hashtable, the execution takes place at low speed.

References

1. https://link.springer.com/article/10.1007/s10664-021-09950-y
2. https://dl.acm.org/doi/abs/10.1145/2851613.2851967
3. https://ieeexplore.ieee.org/abstract/document/5565628/