HashMap vs. Hashtable in Java: Key Differences and Efficiency for Non-Threaded Applications

HashMap and Hashtable are fundamental data structures in Java that store key-value pairs. Understanding their distinctions is crucial for selecting the most suitable option.

Key Differences:

• Synchronization: Hashtable is synchronized, while HashMap is not. Synchronization means that only one thread can access the collection at a time, which makes Hashtable safe for multithreaded environments. However, it introduces overhead in non-threaded applications.
• Null Keys and Values: Hashtable prohibits both null keys and values. HashMap, on the other hand, allows one null key and several null values.
• Deterministic Iteration Order: HashMap preserves the order of insertion when iterating over key-value pairs. Hashtable does not guarantee any specific order.

Efficiency for Non-Threaded Applications:

Since synchronization is not required in non-threaded applications, HashMap is more efficient than Hashtable. Unsynchronized data structures generally have better performance due to reduced overhead.

Recommendation:

For non-threaded applications, where synchronization is not a concern, HashMap is the recommended choice. If deterministic iteration order is important, the subclass LinkedHashMap provides that functionality.

Note:

If synchronization is necessary, a more appropriate option is ConcurrentHashMap, designed for concurrent access environments.