hashCode method
The hashCode method is a Java Object method that returns an integer hash value consistent with the object's equality contract and usable by hash-based collections.
Java Persistence with Spring Data and Hibernate epub
The hashCode method is the Java object method that returns an integer hash value used by hash-based collections.
- How it is used
- Supports value-based set membership for embeddables and equality checks for detached entities.
- How deep it goes
- Works through paired equals() implementations and the lifecycle failure caused by hashing a generated identifier.
- Examples
- Uses an embeddable Image hashed with Objects.hash() and a User hashed by its unique username.
- What you can do after
- Build it from scratch by pairing hashCode() with equals() and choosing hash inputs that remain suitable across persistence transitions.
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100 Java Mistakes and How to Avoid Them
The hashCode method is a Java object method that returns an integer hash value consistent with the object's equality contract.
- How it is used
- Protects equality-based collections and algorithms from hard-to-debug failures caused by inconsistent object comparison.
- How deep it goes
- Works through order-independent and case-insensitive equality cases, then gives generation, normalization, and verification safeguards.
- Examples
- Uses swapped integer fields and case-insensitive Greek sigma strings whose `Set` lookup exposes a broken hash contract.
- What you can do after
- Diagnose/debug with it by recognizing equality rules that require a corresponding symmetric or otherwise matching hash calculation.
Read how 100 Java Mistakes and How to Avoid Them explains hashCode method →
Related concepts
- cryptographic hashcontrasts with · 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.
- hashsetused by · A hash set is a collection of distinct values that uses hashing to support efficient membership testing without associated values.
- hashcontrasts with · hash is Clojure's default hashing function, mapping any object, including nil, to a 32-bit signed integer consistent with Clojure hashing rules for supported values.
- detached stateused by · Detached entity state is the lifecycle state in which an entity instance is no longer associated with a persistence context and its changes are not automatically synchronized with the database.
- uriused by · A URI (Uniform Resource Identifier) is a standardized character sequence that identifies an abstract or physical resource.
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