Difference Wiki

HashMap vs. HashTable: What's the Difference?

Edited by Huma Saeed || By Sumera Saeed || Updated on October 19, 2023
HashMap allows null values and keys; Hashtable doesn't.

Key Differences

A HashMap is a part of the Java Collections Framework, introduced in Java 1.2. It allows for the storage of key-value pairs, and importantly, it permits null values and null keys. This feature can be both advantageous and problematic, depending on use-cases. On the other hand, a Hashtable is a legacy data structure, part of the original version of Java. A Hashtable does not allow null values or null keys. As a result, putting a null value or key into a Hashtable will result in a NullPointerException.
Sumera Saeed
Oct 19, 2023
Another major distinction between HashMap and Hashtable revolves around synchronization. A Hashtable is synchronized, meaning it is thread-safe and can be shared among multiple threads without compromising data integrity. This comes at a cost, as it generally means slower performance compared to unsynchronized structures. Conversely, a HashMap is not synchronized. If multiple thread access is needed, it must be synchronized externally, using methods provided by the Collections framework or other mechanisms.
Sumera Saeed
Oct 19, 2023
Both HashMap and Hashtable implement the Map interface, but due to their respective characteristics, their usage varies in modern Java applications. For instance, because of its non-synchronized nature and ability to handle nulls, HashMap tends to be more popular in single-threaded applications or scenarios where synchronization is managed externally. In contrast, Hashtable, due to its synchronized nature, may be preferred in scenarios where thread safety is a primary concern and performance trade-offs are acceptable.
Sumera Saeed
Oct 19, 2023
While HashMap and Hashtable have differences, they also have similarities. Both structures store key-value pairs and can be used to efficiently retrieve a value based on its key. The decision to use one over the other should be based on specific requirements such as null handling and the need for synchronization.
Harlon Moss
Oct 19, 2023

Comparison Chart

Null Handling

Allows null keys and values.
Doesn't allow null keys or values.
Sumera Saeed
Oct 19, 2023
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Synchronization

Not synchronized (not thread-safe).
Synchronized (thread-safe).
Sumera Saeed
Oct 19, 2023

Performance

Generally faster because it's not synchronized.
Slower due to synchronization.
Sumera Saeed
Oct 19, 2023

Part of

Java Collections Framework (since Java 1.2).
Legacy, from the original version of Java.
Harlon Moss
Oct 19, 2023

Usage in Modern Java

More common, especially in single-threaded apps.
Less common due to legacy status.
Aimie Carlson
Oct 19, 2023

HashMap and HashTable Definitions

HashMap

A member of the Java Collections Framework introduced in Java 1.2.
For modern Java programming, the HashMap is often preferred over Hashtable.
Janet White
Oct 19, 2023
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HashTable

A thread-safe Map implementation due to its synchronized methods.
In multi-threaded scenarios, Hashtable can be a safe choice for data storage.
Sara Rehman
Oct 19, 2023

HashMap

An unsynchronized collection class that offers better performance in single-threaded scenarios.
Since the application is single-threaded, using a HashMap for data storage is ideal.
Huma Saeed
Oct 19, 2023

HashTable

A legacy collection class that has been part of Java since its initial version.
Though Hashtable has been around since early Java days, HashMap is more commonly used now.
Sumera Saeed
Oct 19, 2023

HashMap

A data structure in Java that stores key-value pairs and allows null keys and values.
In the HashMap, the key apple corresponds to the value fruit.
Sumera Saeed
Oct 19, 2023

HashTable

Implements the Map interface, allowing for key-value pair storage and retrieval.
Using a Hashtable, I stored usernames and their associated email addresses.
Sumera Saeed
Oct 19, 2023

HashMap

A mutable structure, allowing for updates, additions, and deletions of key-value pairs.
After adding initial data, I updated the HashMap to include additional entries.
Janet White
Oct 19, 2023

HashTable

A synchronized data structure in Java that stores key-value pairs and prohibits null keys and values.
The Hashtable ensures thread-safety, making it suitable for multi-threaded environments.
Huma Saeed
Oct 19, 2023

HashMap

A Map implementation that uses hashing to store and retrieve objects.
With a HashMap, accessing an object using its key is very efficient due to the underlying hashing mechanism.
Sara Rehman
Oct 19, 2023

HashTable

Uses hashing for internal storage, ensuring efficient data access.
The Hashtable provides quick lookups because of its hashing mechanism.
Sumera Saeed
Oct 19, 2023

HashMap

Alternative spelling of hash map
Sumera Saeed
Nov 12, 2016

HashTable

Alternative spelling of hash table
Sumera Saeed
Nov 12, 2016

FAQs

Between HashMap and Hashtable, which one is synchronized?

Hashtable is synchronized, while HashMap is not.
Sumera Saeed
Oct 19, 2023

Why would one choose HashMap over Hashtable?

HashMap is often chosen for its ability to handle nulls and its unsynchronized nature which offers better performance in single-threaded scenarios.
Aimie Carlson
Oct 19, 2023

Which data structure is more modern in Java: HashMap or Hashtable?

HashMap is more modern as it's part of the Java Collections Framework, while Hashtable is legacy.
Sumera Saeed
Oct 19, 2023

What is a HashMap in Java?

A HashMap is a data structure in Java that stores key-value pairs and can handle null keys and values.
Sumera Saeed
Oct 19, 2023

Is the order of elements preserved in HashMap or Hashtable?

No, neither guarantees order. If order is important, consider using LinkedHashMap.
Sumera Saeed
Oct 19, 2023

Does Hashtable allow null values or keys?

No, Hashtable doesn't allow null values or keys.
Huma Saeed
Oct 19, 2023

Are there alternatives to HashMap and Hashtable in Java?

Yes, there are other Map implementations like TreeMap and LinkedHashMap, each with its own unique properties.
Aimie Carlson
Oct 19, 2023

Can HashMap replace Hashtable in all scenarios?

Not always. While HashMap is versatile, there might be cases where the synchronized nature of Hashtable or other specific features are required.
Harlon Moss
Oct 19, 2023

Why doesn't Hashtable allow null keys or values?

It's a design decision from early Java days to prevent potential issues and NullPointerExceptions.
Harlon Moss
Oct 19, 2023

Can you provide a simple example of how to use a HashMap?

Sure! HashMap map = new HashMap<>(); map.put("apple", 1);
Sara Rehman
Oct 19, 2023

How do you iterate over a HashMap or Hashtable?

You can iterate using methods like keySet(), values(), or entrySet() combined with enhanced for-loops or iterators.
Janet White
Oct 19, 2023

Are there scenarios where Hashtable might be preferred over HashMap?

Yes, in scenarios where thread safety is paramount, Hashtable's built-in synchronization might be preferred.
Sumera Saeed
Oct 19, 2023

Which data structure is generally faster: HashMap or Hashtable?

HashMap is generally faster due to its unsynchronized nature.
Sumera Saeed
Oct 19, 2023

Do both HashMap and Hashtable implement the Map interface?

Yes, both HashMap and Hashtable implement the Map interface.
Harlon Moss
Oct 19, 2023

How do you create a Hashtable in Java?

You can create a Hashtable like this: Hashtable table = new Hashtable<>();.
Janet White
Oct 19, 2023

What are the primary reasons for using HashMap or Hashtable?

Efficient data access and retrieval, flexibility in storing key-value pairs, and the choice of synchronization are primary reasons.
Harlon Moss
Oct 19, 2023

Can a HashMap be synchronized?

Yes, while HashMap is not synchronized by default, it can be synchronized externally using the Collections framework.
Harlon Moss
Oct 19, 2023

How does the internal hashing mechanism work in HashMap and Hashtable?

Both utilize an array of buckets and a hash function to distribute key-value pairs among those buckets, ensuring efficient data access.
Janet White
Oct 19, 2023

What happens if you put a duplicate key in a HashMap or Hashtable?

The new value replaces the old value associated with that key.
Sara Rehman
Oct 19, 2023

How do you remove an entry from a HashMap or Hashtable?

You can use the remove(key) method, providing the key of the entry you wish to delete.
Harlon Moss
Oct 19, 2023
About Author
Written by
Sumera Saeed
Sumera is an experienced content writer and editor with a niche in comparative analysis. At Diffeence Wiki, she crafts clear and unbiased comparisons to guide readers in making informed decisions. With a dedication to thorough research and quality, Sumera's work stands out in the digital realm. Off the clock, she enjoys reading and exploring diverse cultures.
Edited by
Huma Saeed
Huma is a renowned researcher acclaimed for her innovative work in Difference Wiki. Her dedication has led to key breakthroughs, establishing her prominence in academia. Her contributions continually inspire and guide her field.

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