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Add collections module: HashMap bucket layout, treeification, and a real ConcurrentModificationException reproduction

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Companion code for the ankurm.com post "Top 40 Java Collections Interview Questions
(HashMap Internals to Fail-Fast Iterators)". Verified against JDK 25's own HashMap
source (TREEIFY_THRESHOLD=8, UNTREEIFY_THRESHOLD=6, MIN_TREEIFY_CAPACITY=64), with
every claim backed by a committed docs/output/*.txt transcript from a real run.

Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01YXCrLgRKFgCh9RHKW8xaqJ
This commit is contained in:
asmhatre
2026-10-01 04:27:27 +00:00
co-authored by Claude Sonnet 5
commit d4b3a63615
27 changed files with 1085 additions and 0 deletions
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collections/docs/output/05-cme-classic-reproduction.txt
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Classic ConcurrentModificationException: for-each + Collection.remove() mid-loop
================================================================================
list before: [1, 2, 3, 4, 5]
threw: java.util.ConcurrentModificationException
stack trace (trimmed to the ArrayList$Itr frames that matter):
java.util.ConcurrentModificationException
at java.base/java.util.ArrayList$Itr.checkForComodification(ArrayList.java:1096)
at java.base/java.util.ArrayList$Itr.next(ArrayList.java:1050)
at com.ankurm.interviewlab.collections.ConcurrentModificationTest.lambda$classicForEachPlusCollectionRemoveThrows$0(ConcurrentModificationTest.java:28)
at com.ankurm.interviewlab.collections.ConcurrentModificationTest.classicForEachPlusCollectionRemoveThrows(ConcurrentModificationTest.java:27)
at java.base/java.util.ArrayList.forEach(ArrayList.java:1604)
at java.base/java.util.ArrayList.forEach(ArrayList.java:1604)