You may have faced a dilemma about using HashMap or HashTable as both implement similar functionality in Java. This blog focuses on clearing this dilemma and aims to equip you with the knowledge to differentiate between HashMap and HashTable better from now onwards.
In this blog, we will discuss the difference between HashMap and HashTable. We will consider an example as well implementing both HashMap and HashTable. So let’s get started.
HashMap is a data structure in Java that implements the Map interface. It uses a hash table to store key-value pairs, allowing for efficient retrieval, insertion, and deletion of elements. HashMap does not guarantee the order of elements and permits null values for both keys and values.
HashTable is a legacy class in Java that also implements the Map interface. It is similar to HashMap but is synchronized, making it thread-safe. However, this synchronization comes at the cost of performance. It does not allow null values for keys or values.
HashMap and HashTable are both implementations of the Map interface in Java, designed to store key-value pairs, but they exhibit notable differences. One fundamental distinction is in their synchronization behavior. HashMap is not synchronized by default, making it suitable for scenarios where thread safety is not a primary concern, allowing for better performance.
In contrast, HashTable is synchronized, ensuring that all its methods are thread-safe. This synchronization in HashTable is achieved through the use of synchronized methods, but it comes at the cost of increased overhead and potentially reduced performance, especially in scenarios with a high level of concurrent access.
HashMap vs HashTable
Parameter of Differentiation
HashMap
HashTable
Synchronization
Not synchronized by default.
Synchronized; all methods are thread-safe.
Null Values
Permits null values for both keys and values.
Does not allow null values for keys or values.
Performance
Generally offers better performance due to lack of synchronization.
Performance overhead due to synchronization can impact efficiency.
Inheritance
Extends AbstractMap class.
Extends Dictionary class (legacy).
Iterator Fail-Safe
Iterator is fail-fast, detecting concurrent modifications during iteration.
Enumerator is fail-safe, preventing concurrent modifications during enumeration.
Legacy Class
No, HashMap is part of Java Collections Framework.
Yes, HashTable is a legacy class.
Why HashTable Doesn’t Allow null and HashMap Do?
The decision of whether to allow null values in data structures like HashTable and HashMap is influenced by design considerations and the intended use cases of these classes.
In the case of HashTable:
Legacy Design:HashTable is a legacy class in Java that predates the Java Collections Framework. When it was designed, the Java language did not enforce strict null safety, and the use of null values was more flexible. However, the designers of HashTable chose to restrict the use of null values, likely for consistency and to avoid potential issues associated with null references.
NullPointerException Concerns: Allowing null values in HashTable could lead to NullPointerExceptions during key or value retrieval or manipulation. By disallowing nulls, HashTable enforces a stricter contract, requiring non-null keys and values.
On the other hand, in the case of HashMap:
Flexibility and Versatility:HashMap is part of the Java Collections Framework, introduced later with a more flexible and versatile design. The framework embraced the use of null values, providing developers with more freedom in representing data where the absence of a value is a valid state.
Alignment with Java Collections Framework:HashMap follows the conventions of the Java Collections Framework, which allows null values in various contexts. This alignment ensures consistency and familiarity for developers working with collections in Java.
Frequently Asked Questions
What is the difference between HashMap and Hashtable and HashSet?
HashMap and Hashtable store key-value pairs, with HashMap allows nulls and are non-synchronized, while Hashtable is synchronized and doesn’t allow nulls. HashSet only stores unique elements without key-value pairs, internally using a HashMap.
Why Hashtable is faster than HashMap?
Actually, HashMap is generally faster than Hashtable because HashMap is unsynchronized, allowing multiple threads to access it concurrently. Hashtable is synchronized, which introduces overhead, making it slower in multi-threaded environments.
What is the difference between Hashtable and ConcurrentHashMap?
Hashtable is fully synchronized, locking the entire table on updates, while ConcurrentHashMap allows concurrent read and write operations by locking only portions of the map, making it more efficient in multi-threaded environments.
Conclusion
In this blog, we looked in detail about the difference between HashMap and HashTable. This blog also gave a general overview about which one to use between HashMap and HashTable. We also saw an example which showed how similar HashMap and HashTable are in implementation.
If you find this article interesting, please upvote it so that others can find this article easity. Head over to our practice platform Coding Ninjas Studio to practise top problems, attempt mock tests, read interview experiences, and much more.