docs: Java 21 modernization rollup audit - #23

#``# Overview

Migrate COG-GTM/WorldWindJava from Java 11 to Java 21 LTS. This is a federal-grade, zero-breakage migration with atomic per-package PRs, full test verification before and after, and a rollup audit document. Use parallel child sessions to accelerate. All PRs target the fork's develop branch.

#``# PHASE 0: Pre-Migration Baseline (Sequential — MUST complete before anything else)

#``#``# Step 0.1: Capture Pre-Migration Baseline Metrics
Before ANY changes, on the develop branch with JDK 11:

`#` File count
find src -name "*.java" | wc -l
`#` Anonymous inner class counts
grep -rn "new Runnable()" --include="*.java" src/ | wc -l
grep -rn "new ActionListener()" --include="*.java" src/ | wc -l
grep -rn "new Callable()" --include="*.java" src/ | wc -l
grep -rn "new MouseListener()" --include="*.java" src/ | wc -l
grep -rn "new KeyListener()" --include="*.java" src/ | wc -l  
grep -rn "new ChangeListener()" --include="*.java" src/ | wc -l
grep -rn "new PropertyChangeListener()" --include="*.java" src/ | wc -l
grep -rn "new WindowListener()" --include="*.java" src/ | wc -l
`#` instanceof pattern-match candidates
grep -rn "instanceof " --include="*.java" src/ | wc -l
`#` Deprecated usage
grep -rn "`@`Deprecated" --include="*.java" src/ | wc -l
grep -rn "new Integer(" --include="*.java" src/ | wc -l
grep -rn "new Double(" --include="*.java" src/ | wc -l
grep -rn "new Float(" --include="*.java" src/ | wc -l
grep -rn "new Long(" --include="*.java" src/ | wc -l
grep -rn "new Boolean(" --include="*.java" src/ | wc -l

Save all counts to a file BASELINE-METRICS.txt at the repo root. This is your "before" snapshot.

#``#``# Step 0.2: Run the existing test suite under JDK 11

ant -f release-build.xml

Record pass/fail counts. This establishes that the test suite is green BEFORE migration.

#``# PHASE 1: Foundational JDK 21 Retarget PR (Sequential — Wave 0)

#``#``# Step 1.1: Create branch devin/java21-foundation
Make these changes ONLY (no code changes):

1. **`release-... (12653 chars truncated...)

Ran a clean local JDK 21 Ant release build on devin/java21-rollup, verified the full JUnit suite and release artifacts, then ran a Java 21 runtime probe against the built worldwind.jar and worldwindx.jar.

Escalation/caveat: the GUI demo smoke was not fully verified. ./run-demo.bash gov.nasa.worldwindx.examples.HelloWorldWind loaded the built demo class, then JOGL/nativewindow failed under Xvfb with Nativewindow X11 IOError; I treated that as failed/blocked, not a pass. PR #23 still has no configured GitHub CI checks, so this is local/manual verification.

• passed — Clean JDK 21 build: ant -f release-build.xml clean build exited 0 and logged BUILD SUCCESSFUL.
• passed — JUnit totals: 435 tests, 0 failures, 0 errors, 7 skipped.
• passed — Migration gate: 1727 Java files, new Runnable() count 3, new ActionListener() count 7.
• passed — Artifacts: worldwind.jar (7,811,944 bytes), worldwindx.jar (3,343,413 bytes), build/worldwind.zip (119,277,694 bytes), build/doc/worldwind-javadoc.zip (16,114,354 bytes).
• passed — Built-jar runtime probe: Java 21 compiled and ran a probe against the built root jars with exact output version=NASA WorldWind Java v2.2.1, position=34.500,-117.250,1234.5, padded=3x5->4x8, probe=PASS.
• failed/blocked — GUI demo smoke: built HelloWorldWind entrypoint started, then Xvfb/JOGL display handling failed with Nativewindow X11 IOError.

Evidence was captured in this Devin session: https://app.devin.ai/sessions/36287b7c637242dba0a6a659737d5402