How deeply does 100 Java Mistakes and How to Avoid Them cover hash collision?

Demonstrates crafted collisions, bucket treeification, and mutation failure while stopping short of general collision algorithms.

Hash collision

As explained in 100 Java Mistakes and How to Avoid Them

A hash collision occurs when distinct inputs to a hash function produce the same hash value or map to the same hash-table location.

A hash collision occurs when distinct objects produce the same hash value. HashMap and HashSet may treeify a heavily colliding bucket, using compareTo() alongside hashCode() and equals(). section 8.6

A crafted StringBuilder collision

A demonstration creates 40 StringBuilder objects in one bucket, finds another object with a matching hash code, inserts it, and then mutates it. After mutation, contains(sb) returns false because the set can no longer locate the changed key. section 8.6

Avoid collision-related collection failures by:

Keeping objects used as HashMap keys or HashSet elements immutable while stored. section 8.6
Treating identity-based hash codes as implementation-dependent; collision distributions are not guaranteed by the JVM specification. section 8.6

How 100 Java Mistakes and How to Avoid Them covers it

Cover of 100 Java Mistakes and How to Avoid Them

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Also explained in

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Grokking Algorithms, Second EditionA hash collision occurs when distinct keys produce the same hash value or table position.
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Clojure: The Essential ReferenceA hash collision occurs when distinct keys produce the same hash-table index or hash value.
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Software Security for DevelopersA hash collision occurs when two different inputs produce the same hash value.

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Related concepts

hash functionaddressed by · A hash function deterministically maps input data to a value in a bounded output range, commonly for indexing, lookup, comparison, or integrity checking.
birthday attackaddressed by · A birthday attack is a collision-finding method that generates approximately the square root of the hash output space to obtain a substantial probability of matching digests for distinct inputs.
false positiveproduces · A false positive is a result that incorrectly indicates a condition or class is present when it is absent.
machine learningaddressed by · Machine learning is a field of computational methods in which systems learn patterns or relationships from data to make predictions, decisions, or other outputs.
duplex mismatchproduced by · A duplex mismatch is a link condition in which two connected interfaces use different duplex settings or incompatible autonegotiation behavior.

This explainer was generated by Manning's knowledge graph from the text of 100 Java Mistakes and How to Avoid Them. The section links point to the parts of the book it draws on.