Ace Java 2025: Rock Your 'Thinking in Java' Challenge!

Question: 1 / 510

Which concurrent collection class does not permit null elements?

ConcurrentHashMap

CopyOnWriteArrayList

DelayQueue

A ConcurrentHashMap does not allow null keys, but it can store null values.

B: CopyOnWriteArrayList does not allow null elements to be added, but it can store null elements if they are already present.

D: This option is incorrect because while ConcurrentHashMap and CopyOnWriteArrayList may have some restrictions on null elements, the question is specifically about a collection class that does not permit ANY null elements, making DelayQueue the only correct answer.

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