JavaLens

A VS Code extension that generates a live UML class diagram for any Java file you have open, updating as you type.

Features

• Live diagram — re-renders automatically on every edit, no manual refresh needed
• Full UML relationship support:
  • Generalization / Inheritance (--|>) — class A extends B
  • Realization (<|..) — class A implements B
  • Composition (*--) — field instantiated with new X() inline
  • Aggregation (o--) — field type injected via constructor parameter
  • Association (-->) — field reference to another class
  • Dependency (..>) — method parameter, local variable, or return type
• Correct hierarchy layout — parent classes and interfaces render above their children
• Abstract class and interface annotations — <<abstract>> and <<interface>> stereotypes
• Generic type awareness — Map<String, Shape> resolves associations to both Map and Shape
• Dark / light theme — diagram theme follows your VS Code colour theme

Getting Started

Prerequisites

• Node.js (v18+)
• VS Code (v1.85+)

Run in development

git clone https://github.com/<your-username>/JavaLens.git
cd JavaLens
npm install
npm run compile

Then press F5 in VS Code to launch the Extension Development Host.

Use the extension

1. Open any .java file
2. Open the Command Palette (Ctrl+Shift+P)
3. Run JavaLens: Show Class Diagram
4. The diagram panel opens beside your editor and updates as you type

Tech Stack

Layer	Technology
Extension host	TypeScript + VS Code Extension API
Java parser	web-tree-sitter + tree-sitter-java grammar (WASM)
Diagram renderer	Mermaid.js v11 (bundled, no CDN)

Project Structure

src/
  extension.ts   — activation, WebView lifecycle, event wiring
  parser.ts      — tree-sitter Java AST → ClassInfo[]
  serializer.ts  — ClassInfo[] → Mermaid classDiagram syntax
wasm/
  web-tree-sitter.wasm
  tree-sitter-java.wasm
media/
  mermaid.min.js

Roadmap

• Phase 4 — Performance (debounce, incremental tree-sitter parsing)
• Phase 5 — Multi-file / workspace-level diagram
• Toggle dependency arrows on/off
• Zoom and pan controls