Java · Mid-level · Theory

Explain how HashMap works internally, and what happens if you put an object in as a key and then change a field that's used in hashCode.

~4 min by voice

How to approach it

This checks whether the candidate understands HashMap's internals (buckets, hash, collisions, resize) well enough to work out on their own why mutating a key breaks lookups. It also checks whether they know the equals/hashCode contract and the practice of immutable keys.

Have you seen this question in a real interview?

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Topics

collections hashmap

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Answer by voice

The interviewer will ask this question and listen. Think out loud and ask for a hint if you need one. When you're done, pause or tap “That's my answer”. In about a minute, your score and the points you covered show up here.

Best with headphones · ~4 min