What differentiates a Hashtable from a HashMap?

• A. Hashtable is non synchronized
• B. HashMap allows null values
• C. Hashtable is based on a red-black tree
• D. HashMap is synchronized

Answer: (B)

The differentiation between a Hashtable and a HashMap fundamentally lies in their handling of null values, which is well captured by the choice that indicates HashMap allows null values.

HashMap permits the use of one null key and multiple null values, making it a flexible option when managing collections that may include null as legitimate data. In contrast, Hashtable does not accommodate null keys or values at all. This behavior is pivotal in many applications where the presence of nulls needs to be represented and managed effectively.

This characteristic makes HashMap more versatile and easier to work with in modern Java applications, where nullable data is often encountered. Understanding this distinction is essential for developers when selecting data structures based on their specific needs for data integrity and availability of null representations.