Java HashMap Quiz

What is a HashMap in Java used for?

• To store data in key-value pairs.

• To perform mathematical calculations.

• To manage threads.

• To handle exceptions.

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DOK Level 1: Recall

Which of the following is true about a HashMap?

• It maintains the order of insertion.

• It does not allow null keys.

• It is synchronized.

• It allows null values.

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DOK Level 1: Recall

What is the primary difference between HashMap and Hashtable in Java?

• Hashtable is synchronized, while HashMap is not.

• HashMap allows null keys and values, while Hashtable does not.

• Both A and B are correct.

• There is no difference.

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DOK Level 1: Recall

Which method would you use to check if a HashMap contains a specific key?

• get()

• containsKey()

• containsValue()

• size()

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DOK Level 1: Recall

How can you remove a key-value pair from a HashMap?

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DOK Level 1: Recall

What will happen if you try to store a duplicate key in a HashMap?

• It will replace the old value with the new one.

• It will throw an exception.

• It will ignore the new value.

• It will store both values.

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DOK Level 1: Recall

Which of the following is NOT a method in the HashMap class?

• put()

• get()

• insert()

• remove()

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DOK Level 1: Recall

What does the `put()` method in a HashMap return?

• The previous value associated with the key, or null if there was no mapping for the key.

• True if insertion is successful.

• The current value associated with the key.

• None of the above.

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DOK Level 1: Recall

Which collection view can you obtain from a HashMap?

• Keys only

• Values only

• Key-value pairs

• All of the above

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DOK Level 1: Recall

What is the default initial capacity of a HashMap in Java?

• 8

• 12

• 16

• 20

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DOK Level 1: Recall