Hash value
A hash value is a deterministic, typically fixed-size value produced by applying a hash function to input data, often for lookup, comparison, identification, or integrity checking.
Kotlin in Action, 2E
hashCode is an object method that returns an integer hash value consistent with the object's equality semantics.
- How it is used
- Supports equality-aware use of objects as keys or members of hash-based containers.
- How deep it goes
- Defines manual and generated implementations, then warns how mutable keys can invalidate hash-based containers.
- Examples
- Uses a Customer class, a manual name-and-postal-code hash, hash-set lookup, and generated data-class results.
- What you can do after
- Apply hashCode correctly when overriding equals or declare a data class for generated equality and hash behavior.
Effective Data Analysis
A hash code is the fixed-size output produced by applying a hash function to data.
- How it is used
- Uses fixed-size identifiers to join data and recognize unique individuals while keeping sensitive fields away from analysts.
- How deep it goes
- Explains deterministic behavior, sensitivity to small input changes, and security limits, then demonstrates a pandas implementation.
- Examples
- Demonstrates hashed email values in a transactions dataframe and separates original emails into a restricted table.
- What you can do after
- Apply hashing via Python’s hashlib library to pseudonymize sensitive fields and preserve cross-source joins.
100 Java Mistakes and How to Avoid Them
A hash code is an integer value returned by an object's hashCode method for use by hash-based data structures.
- How it is used
- Supports hash-based collection placement and lookup, while exposing precedence and mutability hazards that can degrade performance or lose access.
- How deep it goes
- Explains operator grouping, bucket selection, and mutation effects, but stops short of defining a complete hashCode contract.
- Examples
- Uses packed-coordinate hashing, buffer-capacity arithmetic, mutable lists, BitSet keys, legacy dates, and StringBuilder.
- What you can do after
- Diagnose hash-based collection failures, inspect precedence, preserve intended grouping, and avoid mutating stored keys.
Read how 100 Java Mistakes and How to Avoid Them explains hash value →
Hacking Cryptography
A hash digest is the fixed-size output produced by applying a hash function to input data.
- How it is used
- Uses fixed-size digests to verify passwords and detect accidental data corruption.
- How deep it goes
- Defines deterministic one-way hashing and shows applications, but defers detailed collision, rainbow-table, and length-extension attacks.
- Examples
- Uses password login comparisons, Linux DVD checksums, and corrupted-download scenarios as concrete examples.
- What you can do after
- Apply it via password verification and checksum comparison while recognizing that public digests do not authenticate messages.
Grokking Web Application Security
A hash value is the fixed-size digest produced by applying a hashing algorithm to input data.
- How it is used
- Protects delivered scripts, detects unexpected data changes, and supports password verification without retaining original inputs.
- How deep it goes
- Defines deterministic and one-way behavior, then demonstrates SRI and bcrypt comparisons without detailing hashing-algorithm internals.
- Examples
- Uses an SHA-384 integrity attribute for JavaScript and a salted bcrypt password-checking snippet.
- What you can do after
- Apply it via browser integrity attributes and bcrypt-style password hash comparison.
Read how Grokking Web Application Security explains hash value →
Akka in Action, Second Edition
A hash code is a deterministic numeric value computed from input data for use in partitioning or lookup.
- How it is used
- Routes related messages consistently across Akka routees.
- How deep it goes
- Explains key extraction, hashing, virtual-node selection, and routee selection while noting these internals remain hidden from normal users.
- Examples
- Uses message IDs, Aggregator messages, data enrichment, and data obfuscation to illustrate stable routing.
- What you can do after
- Apply it via Akka consistent-hashing routers to keep equal-key messages on one routee.
Read how Akka in Action, Second Edition explains hash value →
Fabulous Adventures in Data Structures and Algorithms
A hash code is an integer value computed from data to support its placement and lookup in a hash-based data structure.
- How it is used
- Supports efficient Contains operations and supplies the hash component of equality comparers for hash sets and dictionaries.
- How deep it goes
- Explains bucket lookup, equality contracts, mutation hazards, and multi-field construction, but stops short of hashing-function internals.
- Examples
- Uses string buckets, StartsWith limitations, and a directed acyclic word-graph node comparer with ordered edge hashing.
- What you can do after
- Apply it via C#'s HashCode class when implementing GetHashCode for objects compared by hash-based collections.
Read how Fabulous Adventures in Data Structures and Algorithms explains hash value →
Related concepts
- hash functionproduced by · A hash function deterministically maps input data to a value in a bounded output range, commonly for indexing, lookup, comparison, or integrity checking.
- Mapused by · A map is an associative data structure that stores key-value pairs and supports retrieving values by key.
- hashsetused by · A hash set is a collection of distinct values that uses hashing to support efficient membership testing without associated values.
- cryptographic hashproduced by · A cryptographic hash is a fixed-length digest computed from input data by a deterministic function designed to resist preimage, second-preimage, and collision attacks.
- checksumincludes · A checksum is a value computed from data and used to detect unintended changes or corruption by comparison with a reference value or recomputation.
- password hashingused by · Password hashing is the use of a one-way, deliberately costly function to derive values for securely storing and verifying passwords without retaining the original passwords.
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