Mastering Java: The Ultimate Quiz for 'Thinking in Java'

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Dive into the depths of Java with our quiz based on "Thinking in Java, Fourth Edition" by Bruce Eckel. Test your knowledge, solidify concepts, and prepare for certification with challenging questions and insightful feedback.

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Which concurrent collection class does not permit null elements?

  1. ConcurrentHashMap

  2. CopyOnWriteArrayList

  3. DelayQueue

  4. All of the above

The correct answer is: 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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