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Table of contents
1.
Introduction
2.
What is HashMap?
2.1.
Syntax :
2.2.
Example :
2.3.
Java
3.
What is HashTable?
3.1.
Syntax :
3.2.
Example :
3.3.
Java
4.
Difference Between HashMap and HashTable
5.
HashMap vs HashTable
6.
Why HashTable Doesn’t Allow null and HashMap Do?
7.
Frequently Asked Questions
7.1.
Why HashMap is better than Hashtable?
7.2.
Which is faster: HashMap or Hashtable?
7.3.
Why HashMap is preferred?
7.4.
What is a real life example of HashMap?
8.
Conclusion
Last Updated: Mar 27, 2024
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Difference between HashMap and HashTable

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Introduction

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.

Difference between HashMap and HashTable

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.

Also read, Duck Number in Java and  Hashcode Method in Java

What is HashMap?

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.

Syntax :

import java.util.HashMap;
// Declaration
HashMap<KeyType, ValueType> map = new HashMap<>();
// Insertion
map.put(key, value);
// Retrieval
ValueType retrievedValue = map.get(key);

Example :

  • Java

Java

import java.util.HashMap;

class HashMapExample {
public static void main(String[] args) {
// Creating a HashMap
HashMap<String, Integer> ages = new HashMap<>();

// Adding key-value pairs
ages.put("Rahul", 25);
ages.put("Virat", 30);
ages.put("Rohit", 22);

// Retrieving values
System.out.println("Age of Virat: " + ages.get("Virat"));
}
}

Output:

output
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What is HashTable?

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.

Syntax :

import java.util.Hashtable;

// Declaration
Hashtable<KeyType, ValueType> table = new Hashtable<>();

// Insertion
table.put(key, value);

// Retrieval
ValueType retrievedValue = table.get(key);

Example :

  • Java

Java

import java.util.Hashtable;

public class HashTableExample {
public static void main(String[] args) {
// Creating a Hashtable
Hashtable<String, Integer> ages = new Hashtable<>();

// Adding key-value pairs
ages.put("Science", 85);
ages.put("Math", 90);
ages.put("IT", 100);

// Retrieving values
System.out.println("Marks in IT: " + ages.get("IT"));
}
}

Output:

output

Difference Between HashMap and HashTable

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

Why HashMap is better than Hashtable?

HashMap is preferred over Hashtable for its improved performance, flexibility, and allowance of null values. It is part of the Java Collections Framework, providing modern and versatile functionality.

Which is faster: HashMap or Hashtable?

HashMap is not synchronised, therefore it's faster and uses less memory than Hashtable.

Why HashMap is preferred?

HashMap is preferred for its better performance, flexibility, and versatility. It's not synchronized by default, allowing efficient operations, and it allows null values.

What is a real life example of HashMap?

A real-life example of HashMap is a phonebook where names (keys) are associated with phone numbers (values), facilitating quick and efficient lookups.

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.

Recommended Readings:


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