Java & the JVM · topic 2 of 6
Java Collections
List/Set/Map internals, HashMap, ConcurrentHashMap, performance.
Questions below are grouped from foundations to advanced. Work top to bottom if the topic is new to you, or jump to a level if you are brushing up.
- Questions
- 23
- Difficulty mix
- 4 easy · 13 medium · 6 hard
Topics covered
- ConcurrentHashMap6
- Performance5
- Iterators3
- HashMap Internals3
- List2
- List vs Set vs Map1
- Set1
- TreeMap1
- Sequenced Collections1
Foundations
Easy · 4 questionsDefinitions and building blocks — start here if the topic is new to you.
Core concepts
Medium · 13 questionsThe questions most interviews spend their time on: how it works and when to use it.
Advanced
Hard · 6 questionsInternals, trade-offs and edge cases — useful for senior rounds and follow-ups.
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