J2ME-GO

A Go rewrite of the previous TypeScript-based J2ME-For-Web project for running J2ME MIDlets on modern platforms.

---

What it is

J2ME-GO is a hobby J2ME virtual machine written in Go.

It is the Go successor to the earlier TypeScript implementation, with the same broad goal: boot real J2ME bytecode, bridge enough CLDC/MIDP APIs to run MIDlets, and make classic mobile games playable again in a modern browser.

Unlike the TypeScript version, this project pushes more of the VM and runtime into Go and uses Go WebAssembly as the browser-facing execution target.

---

Current Status (2026-08-02)

Component	Status	Details
Class-file loader	✅ Working	Parses constant pool, fields, methods, and attributes
Interpreter core	✅ Working	Executes a substantial subset of JVM bytecode needed by current tests and sample MIDlets
Runtime model	✅ Working	Java classes, objects, arrays, shadow classes, exceptions, and method area
Native bridge	✅ Working	Registry-based native dispatch for java.lang, java.io, LCDUI, RMS, game APIs, and Nokia APIs
MIDP / LCDUI	🟡 In Progress	Display, Canvas, Graphics, Form, commands, and input are wired up, but game compatibility is still uneven
RMS / Resources	🟡 In Progress	RecordStore and resource loading work for multiple sample games, with edge cases still being filled in
Browser / WASM runner	✅ Working	Web loader, debug page, keyboard input, canvas flushing, and MIDlet boot pipeline are available
Game compatibility	🟡 In Progress	Asteroids reaches visible, keyboard-driven 2D play; other MIDlets are used as compatibility samples
Automated tests	✅ Passing	go test ./... is green

---

Recent Progress (2026-08-02)

• 2D MIDP compatibility is the active focus

  • Added float/double JVM instructions, local variables, arrays, and conversions
  • Added common floating-point java/lang/Math APIs
  • Added LCDUI List shadow inheritance from Displayable
  • Added a silent J2ME Media API compatibility backend, so optional audio no longer blocks 2D game startup
  • M3G / JSR-184 3D is explicitly deferred rather than driving the core runtime roadmap

• Asteroids is the current 2D reference sample

  • It renders, advances frames, and accepts keyboard input in the browser
  • High-volume runtime logs were removed from the browser DOM path to protect frame performance

• 智力方块 now reaches its visible LCDUI menu

  • Its standard List is bridged to the Canvas renderer and produces non-black browser frames
  • Menu input and command activation remain the next compatibility step

• The browser debugging loop is usable for real game bring-up

  • MIDlet loading from the web page works
  • 宠物王国4、宠物王国5与怪兽仙境3已加入选择器，作为 RPG 资源与运行时兼容样本
  • 宠物王国5已补 Nokia DirectUtils / DirectGraphics.setARGBColor / drawImage / fillPolygon 的最小 2D 桥接；下一步是浏览器首帧回测，不涉及新的渲染后端
  • 怪兽仙境3已到 startApp()，目前阻塞于其私有资源包格式；这不是 Go 或 2D 渲染性能问题
  • Canvas flushing and non-black frame detection are in place
  • Runtime logs make it practical to chase compatibility gaps one by one

---

Quick Start

Prerequisites

• A recent Go toolchain with WebAssembly support
• Python 3
• A modern browser

Installation

git clone https://github.com/lingfeng11111/J2ME-GO.git
cd J2ME-GO

go test ./...
make build-wasm
make serve-web

Then open http://localhost:8080.

Running a MIDlet

1. Build the WASM target with make build-wasm
2. Start the local web server with make serve-web
3. Place your own MIDlet JAR in web/ locally
4. Open the debug page and load the MIDlet in the browser

---

Project Layout

cmd/
├─ j2me-go/              # Desktop entry
└─ j2me-go-wasm/         # Browser / WASM entry

pkg/
├─ classfile/            # Java class-file parser
├─ interpreter/          # JVM bytecode interpreter
├─ runtime/              # Java classes, objects, arrays, exceptions, loaders
├─ native/               # Native method registry and platform bridges
└─ midp/                 # MIDP graphics, display, canvas, RMS, resources

web/
├─ index.html            # Browser debug loader
├─ wasm_exec.js          # Go WASM runtime shim
├─ batch_test.js         # Browser-side test helpers
└─ serve.sh              # Local serving helper

tests/
├─ classfiles/           # Small Java test programs and compiled fixtures
└─ src/                  # Test source files

---

Key Features

• Go-first VM architecture: parser, interpreter, runtime, and native bridge are implemented in Go
• Browser target: runs through Go WebAssembly with a Canvas-based rendering path
• Shadow-class approach: missing Java ME platform classes can be modeled incrementally
• Compatibility-driven development: real MIDlets are used to expose missing runtime behavior
• Test-backed core: parser, interpreter, runtime, MIDP, and native layers all have Go tests

---

Why?

Because flip-phone Java games are too interesting to leave trapped in old hardware.

And because rewriting a VM twice, first in TypeScript and then in Go, is exactly the kind of unreasonable idea that occasionally turns into a good project.

---

Acknowledgments & Inspiration

The earlier TypeScript project, J2ME-For-Web, established the direction for this rewrite.

This repository also benefited from studying older J2ME browser efforts and existing reference implementations such as Mozilla's PluotSorbet, along with other open J2ME projects used for comparison and debugging.

---

Contributing

Issues and pull requests are welcome.

If you want to work on compatibility, the most useful path is usually:

1. Pick one failing MIDlet behavior
2. Reproduce it in the browser runner
3. Trace the missing bytecode, runtime class, or native method
4. Add a focused test when possible