# vigna/fastutil

fastutil extends the Java™ Collections Framework by providing type-specific maps, sets, lists and queues.

Repository: https://github.com/vigna/fastutil
Canonical: https://ross.abutalabs.com/products/fastutil
Language: Java
License: Apache-2.0
License Family: permissive
Topics: primitive-collections, sorting-algorithms, java
Last push: 2026-07-22T22:00:40+00:00

## Health v2 (maintenance only)
Score: 74/100 (v2, computed 2026-09-03T02:20:16.233290+00:00)
- activity 93, release rhythm 35, longevity 100
- inputs: {"age_days": 4132, "days_push": 42, "days_rel": null, "gap_med": null, "n_releases_24m": 0}
- flags: no_releases
- formula: round(0.45*activity + 0.35*rhythm + 0.20*longevity); archived -> min(score, 10)

## Adoption (not part of the score)
Stars 2230, forks 230 (observed 2026-08-28T04:06:29.028678+00:00)

## What it is
fastutil is a Java library that extends the Java Collections Framework with type-specific maps, sets, lists, and queues for primitives and references, offering small memory footprint and fast access. It also provides 64-bit big arrays and fast binary/text I/O classes.

## Use cases
- store large collections of primitive ints without boxing overhead
- reduce memory footprint of maps and sets in a Java application
- use 64-bit indexed big arrays larger than 2^31 elements
- read and write binary files quickly in Java
- replace HashMap with a faster primitive-keyed map
- sort primitive arrays efficiently

## When to choose
- your Java code is bottlenecked by autoboxing or standard collection memory overhead
- you need collections keyed or valued by primitives with standard Map/Set interfaces
- you need big arrays exceeding integer index limits

## When to avoid
- your collections are small and performance is not critical
- you want a minimal dependency footprint without using the core jar or a minimized jar
- you are not on the JVM

## Facets
- artifact type: library
- maturity: stable
- function: serialization, file-system, developer-tools
- domain: developer-tools, performance
- platform: jvm
- tags: primitive-collections, java-collections, memory-efficiency, big-arrays, sorting-algorithms, algorithms

## Member repositories
- vigna/fastutil (main) score 74

## Provenance
- Observed fields: from GitHub, fetched 2026-08-28T04:06:29.028678+00:00.
- Health v2: computed from the inputs above; adoption is never an input.
- Inferred fields (summary, facets, guidance): AI-extracted, prompt v1, taxonomy v1, on 2026-08-30T02:44:39.006100+00:00, confidence not recorded.
  - readme: https://github.com/vigna/fastutil (fetched 2026-08-28T04:06:29.028678+00:00, sha 5d54c8d27f92)
- Data as of 2026-08-30T08:39:29.467469+00:00.