# Guava — Google Core Libraries for Java

> Google's suite of core Java libraries covering collections, caching, primitives, concurrency, common annotations, string processing, I/O, and more.

## Install

Save as a script file and run:

# Guava — Google Core Libraries for Java

## Quick Use
```xml
<dependency>
  <groupId>com.google.guava</groupId>
  <artifactId>guava</artifactId>
  <version>33.4.0-jre</version>
</dependency>
```
```java
import com.google.common.collect.ImmutableList;
ImmutableList<String> items = ImmutableList.of("a", "b", "c");
```

## Introduction
Guava is Google's open-source set of core Java libraries that supplement the standard library. It grew out of Google's internal Java codebase and provides battle-tested utilities used across thousands of production services.

## What Guava Does
- Provides immutable collections (ImmutableList, ImmutableMap, ImmutableSet) that prevent accidental mutation
- Offers a powerful in-process caching API (LoadingCache, CacheBuilder) with size and time-based eviction
- Includes utilities for concurrency such as ListenableFuture and RateLimiter
- Supplies string utilities (Splitter, Joiner, CaseFormat) and precondition checks
- Adds functional-style helpers, hashing (Murmur3, SHA), I/O helpers, and math utilities

## Architecture Overview
Guava is a single JAR of pure Java with zero transitive dependencies. It is organized into packages by domain: com.google.common.collect for collections, com.google.common.cache for caching, com.google.common.util.concurrent for concurrency, and so on. Each package is self-contained and follows Google's strict API compatibility guarantees.

## Self-Hosting & Configuration
- Add the Maven or Gradle dependency; no external service required
- Choose the `-jre` artifact for Java 8+ or `-android` for Android and older JVMs
- Configure caching via CacheBuilder with maximumSize, expireAfterWrite, or expireAfterAccess
- Use @Beta-annotated APIs with caution as they may change between releases
- Guava follows semantic versioning; deprecated APIs are removed after a deprecation period

## Key Features
- Immutable collections that are inherently thread-safe and memory-efficient
- LoadingCache with automatic loading, eviction policies, and statistics
- ListenableFuture and Futures utilities for composable async programming
- RateLimiter for smooth client-side rate limiting
- EventBus for lightweight publish-subscribe within a JVM process

## Comparison with Similar Tools
- **Apache Commons Lang** — focuses on java.lang extensions; Guava covers a broader surface including collections and caching
- **Eclipse Collections** — richer primitive collections but lacks Guava's caching and concurrency utilities
- **Caffeine** — superior standalone cache (inspired by Guava Cache) but does not provide collections or I/O helpers
- **Vavr** — functional collections for Java; heavier API surface and learning curve

## FAQ
**Q: Is Guava still actively maintained?**
A: Yes. Google releases multiple updates per year and uses Guava extensively in production.

**Q: Should I use Guava Cache or Caffeine?**
A: For new projects, Caffeine is recommended for pure caching. Guava Cache is adequate for existing codebases already depending on Guava.

**Q: Does Guava work with Java 21+?**
A: Yes. The -jre artifact supports the latest LTS Java versions.

**Q: What is the difference between -jre and -android artifacts?**
A: The -jre artifact targets Java 8+ and includes APIs using newer JDK types. The -android artifact avoids those for compatibility with Android and older runtimes.

## Sources
- https://github.com/google/guava
- https://guava.dev/

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Source: https://tokrepo.com/en/workflows/d6d9fb6f-433e-11f1-9bc6-00163e2b0d79
Author: Script Depot