🧩 JSpecify Nullness Exercise

Motivation

This project is a hands-on introduction to JSpecify — the emerging standard for nullness annotations in Java.
The goal is to get comfortable with @NullMarked, @Nullable, and the semantics behind them, while learning how tools like Error Prone interpret null-safety contracts.

You’ll start from partially annotated code, fill in the missing pieces, and verify your understanding by comparing your work with the provided solution.

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Setup

The repository has two branches:

Branch	Description
main	Starting point — incomplete or incorrectly annotated code
solutions	Fully annotated, correct version for comparison

Your task is to complete the annotations (and in a few spots, small method implementations) so that the build passes under Error Prone.

💡 IntelliJ may only show warnings, but the Gradle build is configured to fail if nullness issues are detected.

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Plan

1. Read the JSpecify documentation
   👉 https://jspecify.dev

2. Clone and open the project

   git clone https://github.com/JurenIvan/jspecify-exercise.git
   cd jspecify-exercise

3. Check out the starting branch

   git checkout main

4. Run the build

   ./gradlew build

   It should pass.

5. Add nullness annotations
   Fix the nullness issues by applying the correct @NullMarked, @Nullable, and related annotations.
   Some classes may also require a tiny implementation of methods. It's could give you the feel for guardrails JSpecify provides.

6. Commit your solution

   git checkout -b my-solution
   git commit -am "My JSpecify solution"
   git push origin my-solution

7. Create a Merge Request
   Open a Merge Request (or Pull Request) to the solutions branch.
   You’ll then see a clear diff against the reference solution to check your work.

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Style considerations

Project uses intelliJs defaults for formatting, importing etc. When implementing:

• Try to use minimal number of annotations (to have code as concise as possible)
• Consider each class as a separate entity (don't do package-info.java)

To avoid having unnecessary diff to the solution branch.

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Build Configuration

The project uses Gradle with Error Prone and NullAway enabled.
They enforce nullness correctness — builds fail when annotations are missing, misplaced, or inconsistent.

If you have any issues running it. Help me streamline this exercise.

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Good luck! 🍀

Take your time to read the JSpecify docs (I found their userguide to be amazing!), reason about null contracts carefully — it’s excellent practice for writing robust, null-safe Java.
When you’re done, open your MR and compare your work against the solutions branch.
You’ll know exactly how close you got. 🚀