java
9 minJava equals and hashCode: Fix Broken HashMap and HashSet Lookups
Diagnose collection bugs caused by inconsistent equality, mutable keys, inheritance, and accidental identity comparisons.
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4 matching resultsArticles and interview answers
Q&A
Q&AWhy can a HashMap fail to find a key that was inserted?
Mutable key fields or inconsistent equals/hashCode behavior can make lookup search a different bucket.
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HashMap uses hashCode to choose a bucket and equals to identify a key within it. Equal values must share a hash, and hash-relevant state must not change while the object is used as a key. Check equality in both directions, inspect hash values, and prefer immutable key objects.
Q&A
Q&AWhat happens when two Java HashMap keys have the same hash code?
The keys share a bucket, then equality distinguishes entries within that bucket.
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A hash helps select a bucket but does not establish key identity. HashMap checks equality among entries in the bucket; collisions can be stored in a list and, in sufficiently large bins, treeified under implementation conditions. Correct equals/hashCode behavior is essential, and resizing changes bucket placement without making hashes unique.
devops
5 minDevOps Foundations: Safe Changes, Health Signals, and Rollback Boundaries
Design a release as a controlled change to code, configuration, and data, with explicit health checks and a recovery plan that matches what can actually be reversed.