google/guava — reverse-engineered prompt

Build me a solid Java core utilities library that developers can drop into normal Java projects. I want it to feel like a trusted toolbox for everyday coding, not an app with a UI.

It should include useful collection helpers like immutable lists and maps, multimaps, multisets, and basic graph support. Add practical utilities for strings, primitives, hashing, file and stream I/O, and simple concurrency helpers for working with futures. Please make the public API clean and stable, with good names and examples that make it easy to understand.

Set it up as a Maven based project that can publish a jar, with tests covering the important behavior. It should work on JDK 8 or newer, and please keep an Android compatible version in mind where that affects the design.

Also add a clear README showing how to use it from Maven and Gradle, plus a few short examples. Look up current Java docs online if you need to.