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Difference Between HashMap and HashTable in Java

Both HashTable and HashMap are hashing techniques that store unique keys. In this article, we will discuss the difference between HashMap and HashTable. But let us first know more about them individually.

They primarily store data in value/key pairs in a hash table. When using both of these, you can specify the object used in the form of a key. You can then also specify the value that you want to link to it. When storing the data, we use hashing to hash the key and use the resulting hash code in the form of the index (to store the value within the given table). HashTable and HashMap are very crucial classes in a Java collection framework. There are still various differences between them.

What is a HashMap?

It is a collection class of Java that is Map-based- used for storing data keys in Value and Key pairs. The HashMap assists in the process of implementation of Java Map interface. It is Java’s collection part since version 1.2, and one must know its Key to access the value that resides in it.

Since it uses a technique named Hashing. Thus, it is known as HashMap. The process of Hashing converts large strings into very smaller ones while still keeping the String’s value constant. The compressed value that results from it assists in faster searches as well as indexing.

What is a HashTable?

It is a data structure type that stores the pairs of keys/values. It stores data in an array format. Out of this, every data value holds a unique index value of its own. A user can easily access data very fast if they are aware of the index of the data they desire. The class of Java HashTable implements a hashtable that functions to map the keys into values. This hashtable inherits the Dictionary class, and it also implements the interface of the Map.

Difference Between HashMap and HashTable in Java

Parameter HashMap in Java HashTable in Java
Introduction The HashMap is an advanced version of the HashTable. It was introduced as a type of new class in the JDK 1.2. On the other hand, the HashTable is the legacy class. It was introduced before the HashMap.
Internal implementation Both of their internal implementations are the same up to some extent. The only difference is that in the case of HashMap, it allows multiple null values and one null key. The implementation of a HashTable is internal in such a way that it allows no null value or null key.
Synchronization The HashMap stays non-synchronized. It is because it is not very thread-safe. A user can’t share it between various threads with a proper set of synchronization codes. The HashTable stays synchronized. It is because it is thread-safe. One can share it with various threads.
Null Values It allows multiple null values with one null key. It doesn’t allow any null value or key.
Traversing of Elements You can traverse a HashMap by Iterator. The HashMap provides a user with an Iterator for the process of iteration for traversing all the stored values. On the other hand, you can easily traverse the values stored in a HashTable by Iterator along with an Enumerator.
Process of Synchronization A user can synchronize the HashMap by calling a specified code. An unsynchronized HashTable does not exist because it stays synchronized internally.
Inheritance It inherits a class named AbstractMap. It inherits a class named Dictionary.
Performance of Index The HashMap works very fast compared to the HashTable. It is because of the absence of any synchronization in it. The HashTable works very slow as compared to the HashMap. It is because of the presence of synchronization. But in this case, one doesn’t have to write an extra code for obtaining synchronization.
Class It is a new type of class that was introduced in JDK 1.2. It is a type of legacy class.
Fail-Fast The Iterator present in HashMap is fail-fast. The Enumerator present in a HashTable is not fail-fast.

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