HashMap vs. Hashtable in Java: When Should I Use Which?

Distinguishing HashMap and Hashtable in Java: Performance and Features

Understanding the differences between HashMap and Hashtable is crucial for optimal performance in Java applications. Both are data structures used for mapping keys to values, but they exhibit distinct characteristics and synchronization behaviors.

1. Synchronization

The primary distinction lies in synchronization. Hashtable is synchronized, which means its methods are thread-safe. This ensures that concurrent access to the Hashtable is handled appropriately, preventing data corruption. In contrast, HashMap is not synchronized, making it less suitable for multithreaded environments.

2. Null Values

Hashtable prohibits null keys and values, while HashMap permits one null key and multiple null values. This flexibility in HashMap allows for more scenarios, such as representing a missing value.

3. Iteration Order

HashMap doesn't maintain a specific iteration order, but LinkedHashMap, a subclass of HashMap, provides predictable iteration order. Hashtable, on the other hand, lacks such an alternative.

Recommended Choice for Non-Threaded Applications

Since synchronization is not a concern in non-threaded applications, the best choice is HashMap. Its lack of synchronization overhead results in faster performance compared to the synchronized Hashtable.

Consideration for Multithreaded Environments

If synchronization becomes a requirement, the ConcurrentHashMap class offers a synchronized implementation of a HashMap, providing both thread safety and efficient performance.

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