HashTable vs HashMap

In this comparison, we explore the differences between HashTable and HashMap, two commonly used data structures in Java for storing key-value pairs. HashTable is thread-safe, meaning it can be used safely in concurrent applications, but it does not allow null keys or values and is slower due to synchronization overhead. HashMap, on the other hand, is not thread-safe and requires manual synchronization for concurrent use, but it allows one null key and multiple null values, offering better performance in single-threaded scenarios. This summary helps you decide which data structure to use based on your specific needs for thread safety and performance.

7/26/20241 min read

gray laptop computer on brown wooden desk

gray laptop computer on brown wooden desk

HashTable vs HashMap

What They Are:

HashTable: A data structure that stores key-value pairs. It is synchronized and thread-safe.
HashMap: A data structure that also stores key-value pairs. It is not synchronized and not thread-safe.

Key Differences:

Thread Safety:
- HashTable: Thread-safe. Multiple threads can safely access it at the same time.
- HashMap: Not thread-safe. If multiple threads access it simultaneously, you need to handle synchronization manually.
Synchronization:
- HashTable: Synchronized methods for thread safety.
- HashMap: No built-in synchronization.
Null Keys and Values:
- HashTable: Does not allow null keys or values.
- HashMap: Allows one null key and multiple null values.
Performance:
- HashTable: Slower due to synchronization overhead.
- HashMap: Faster as it does not have synchronization overhead.
Use Cases:
- HashTable: Use when thread safety is a concern and you don't want to handle synchronization manually.
- HashMap: Use when you do not need thread safety, or when you handle synchronization externally.
  
  Simple Java Code Examples:
  1. HashTable Example:

2. HashMap Example: