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Java 24 Round-Trip Showcase

The most complex step in the example ladder (ArrayLang → Java 8 → Java 24; see ../README.md). Parses a real Java 24 source file into a typed VMF model, proves the unparse is byte-identical, then applies one surgical model edit and shows that exactly one line changes.

What it demonstrates:

  • A real-world grammar, unchanged. The 1000-line labeled Java 24 grammar (records, sealed types, pattern switches, text blocks; based on ANTLR grammars-v4) — VMF-Text generates the complete typed model + parser + unparser API from this single file.
  • Exact lexical preservation. All comments, blank lines and irregular formatting survive parse → unparse byte-for-byte.
  • Surgical edits. methodDecl.getMethodName().setText("render") changes exactly one token in the output; every other byte stays untouched.

Run it

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

./gradlew run

Expected output (abridged):

[1] sample/Shapes.java (955 chars) round-tripped byte-identically
  line 27  -     static String describe(Shape shape) {
  line 27  +     static String render(Shape shape) {
[2] one model edit -> one changed line; every other byte is untouched

Layout

  • src/main/vmf-text/demo/java24/Java24.g4 — the labeled Java 24 grammar (copied from the VMF-Text test suite; only the @DelegateTo package names were adjusted)
  • src/main/java/demo/java24/ — small support classes referenced by the grammar (the superClass parser base and two @DelegateTo behaviors) plus the Main showcase
  • sample/Shapes.java — the input file; edit it and re-run to test your own snippets

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).