Java collections under load
Free Java collections module: HashMap races, ConcurrentHashMap, and LRU under write load. First topics open in the browser — no sign-up.
Free Core Java module on HashMap, ConcurrentHashMap, LRU, and collections that fail when many threads write. No account to start.
HashMap is not safe for concurrent writes. ConcurrentHashMap is not a drop-in for every Map contract. Interviewers ask resize, equals/hashCode, and LRU eviction because those bugs show up in caches and session maps.
This guest module is the collections track with the first topics unlocked. Pair it with the Kafka lab if you care about ordering, and with JVM memory if the structure itself is the leak.
What you will cover
- HashMap resize and concurrent write failure
- ConcurrentHashMap vs Collections.synchronizedMap
- equals and hashCode contracts in HashSet
- LRU and LinkedHashMap access order
- First topics free in the browser
Related free labs and modules
Common questions
Can I learn Java collections without an account?
Yes. This module opens HashMap, ConcurrentHashMap, and LRU topics as a guest. Sign in for the rest of the Java collections track.
Why does HashMap break under concurrent load?
Unsynchronized HashMap can corrupt buckets during resize. Concurrent writes can loop or drop entries. Use ConcurrentHashMap or an explicit lock when multiple threads mutate the map.
Is this a full Java collections course?
It is the same module paid users study, with a guest preview of the first topics. The full track, quizzes, and saved progress need a free account.
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