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Add Java as a playable language

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
55/100
Issue type
Feature
Clarity
Clearly specified
Activity status
Active
Tech stack
java, javascript
Domain
backend, testing

Research direction

Start with backend/arena/runner/harness.js, reading pythonProgram and javascriptProgram, LANGUAGES, and starterCode; then inspect backend/tests/ for existing runner tests. Add the Java driver, supported typed starter code, and Judge0 id, then verify representative correct and incorrect solutions against Judge0, run npm test, and run node scripts/check-boundary.js.

Written by the indexing model from the issue text.

Description

help wanted

Most requested for interview-style practice. Java has no tuple type, so problems with mixed tuples may be left out for Java (see below).

CodeArena runs player code in Python, JavaScript and TypeScript. Adding a language is self-contained and a great way to get into the codebase.

Where the code lives

  • backend/arena/runner/harness.js: one small driver per language. The driver reads {"tests":[{"args":[...]}]} as JSON on stdin, calls the player's function once per test, and prints the per-run marker line followed by a JSON array of { ok, value } / { ok, error }. Copy the shape of pythonProgram / javascriptProgram. The marker nonce must stay per-run.
  • LANGUAGES in the same file: add { label, judge0Id }.
  • starterCode(problem, language): typed starter code built from problem.function (name, params[].type, returns).
  • backend/arena/runner/executors.js: localExecutor only knows node and python3; add your compiler for local development if you like (it is never used in production).

Types the 45 problems use

integer, integer[], integer[][], number[], string, string[], boolean, and tuples: [integer, integer], [integer, integer][], [integer, integer, integer][], [string, integer][], [string, string, string][], [integer, integer, string].

Statically typed languages need a mapping for each of these. If a mixed tuple such as [string, integer] has no clean equivalent in your language, it is fine to leave that problem out for your language rather than force an awkward type: the loader supports per-problem languages via runnableLanguages.

Definition of done

  • Driver plus typed starter code for every problem your language supports.
  • Judge0 language id wired up (Judge0 CE: Java 62, C++ 54, Go 60; confirm on your Judge0 instance).
  • Proof: correct solutions pass and wrong ones fail on a spread of problems (easy, medium, hard, and every type above) against a real Judge0 (docker-compose.judge0.yml in the repo root runs one locally).
  • Tests in backend/tests/ covering the driver output and starter code; npm test stays green.
  • node scripts/check-boundary.js passes.
Dominant language
JavaScript
Stars
0
Forks
2
No merged PRs in 30d

Getting set up

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

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