Difference Between HashMap and Hashtable (With Table)

HashMap is performing 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.

HashMap vs Hashtable

The difference between HashMap and Hashtable is that HashMap enables duplicate values for both key and values, whereas, Hashtable does not enable any duplicate value for both key 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 of multiple threads as it does not enable multiple threads to approach them.

Comparison Table Between HashMap and Hashtable

Parameters of comparison HashMap Hashtable
ConcurrencyHashMap 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.
SpeedThe HashMap execution takes place at high speed.The Hashtable execution takes place at a very slow speed.
Null value acceptanceHashMap accepts null values for both key and values. Hashtable does not enable any null value for both keys and values.
IteratorIterator is fail-fast and sometimes throws ConcurrentModificationException.The enumerator is not fail-fast and does not throw any ConcurrentModificationException.
Class InheritanceAbstractMap class.Dictionary class.
ApplicationHashMap 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. 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, 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 empty the HashMap with a specified initial capacity and a load factor.

HashMap is not concurrent. Hence they mostly enable multiple threads approaching 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 often 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 table, game programs as transposition table, and online spelling checkers.

Main Differences Between HashMap and Hashtable

  1. HashMap is not concurrent. Hence they enable multiple threads approaching, whereas, Hashtable is concurrent and does not enable multiple threads to approach them.
  2. 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.

Conclusion

Both HashMap and Hashtable are the basic map interface execution in java. HashMap is a box that reserves a collection of key or value pairs that does not contain any duplicate values. In HashMap, a key and its value that is reserved forms an entry, and the entries present in them are not ordered, and mostly they have high execution speed. Hashtable maps keys to the values and keeps in check the declared variables in java, and it has low execution speed due to its non-organized nature.

Both HashMap and Hashtable have many similar functions, yet they are different in many aspects. HashMap and Hashtable have many useful applications, such as they are used in web pages, web applications, game programming, compilers, and online spelling checkers.

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/
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