java8-roundtrip

Java 8 Round-Trip Showcase

A small, real Java grammar example: parse a short Java 8 source file into a typed VMF model, prove the unparse is byte-identical, then replace a method name and a string literal on the model — every other byte stays untouched.

What it demonstrates:

• A full language grammar. The labeled Java 8 grammar (based on ANTLR grammars-v4) generates the complete typed model + parser + unparser API.
• Exact lexical preservation. Comments, blank lines and irregular formatting survive parse → unparse byte-for-byte.
• Value replacement. setMethodName("sayHello") and setStringValue("\"hello, world\"") change exactly those tokens.

Run it

Requires JDK 21. Everything resolves from Maven Central — no local builds:

./gradlew run

Expected output (abridged):

[1] sample/Greeter.java (… chars) round-tripped byte-identically
  line 13  -   public static void greet( String[] args ){
  line 13  +   public static void sayHello( String[] args ){
  line 14  -     System.out.println( "hello" );   // trailing comment
  line 14  +     System.out.println( "hello, world" );   // trailing comment
[2] two model value edits -> two changed lines; every other byte is untouched

Layout

• src/main/vmf-text/demo/java8/Java8.g4 — the labeled Java 8 grammar (copied from the VMF-Text test suite; only the @DelegateTo package names were adjusted)
• src/main/java/demo/java8/ — @DelegateTo support classes plus Main
• sample/Greeter.java — the input file; edit it and re-run

This is step 2 of the example ladder (ArrayLang → Java 8 → Java 24). See ../README.md.

Note: ANTLR Tool version ... does not match the current runtime version warnings during generation are harmless (tool/runtime alignment lands with VMF-Text 0.2.1).