Java — Which collection class allows key-value associations and provides synchronization?

Introduction / Context:
This checks knowledge of synchronized collections and legacy classes.

Concept / Approach:

• Hashtable is synchronized, meaning its methods are thread-safe.
• It stores key-value pairs like HashMap but synchronizes all methods.
• TreeMap → ordered keys, but not synchronized.
• SortedMap → interface, not a class.
• TreeSet → stores unique values, not key-value pairs.

Final Answer:
java.util.Hashtable