Hashtable nullability rule — can a key be null and can a value be null?
C# Programming
Collection Classes
Difficulty: Easy
Choose an option
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ATrue — a key cannot be null, but a value can be null.
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BFalse — both key and value can be null.
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CFalse — neither key nor value can be null.
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DFalse — a key can be null, but a value cannot be null.
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EIt depends on the comparer used.
Answer
Correct Answer: True — a key cannot be null, but a value can be null.
Explanation
Introduction / Context:Hashtable stores key/value pairs with hashing semantics. Null handling differs for keys and values.
Concept / Approach:Hashtable prohibits null keys because hashing and equality logic require a valid object reference. However, values may legitimately be null to represent “no value” while still reserving a key in the table.
Why Other Options Are Wrong:Allowing a null key breaks hashing; disallowing null values is unnecessary; the comparer does not change the prohibition on null keys.
Final Answer:True — a key cannot be null, but a value can be null.