# migration-17-25

Companion module for the ankurm.com post *Java 17 to Java 25 Migration Guide: The Direct Jump*.

The probes in `src/probes/` are compiled **once** with JDK 17 (`--release 17`) and run unchanged on JDK 17.0.20.1 and JDK 25.0.4.1, which is what a team skipping 21 actually does. `src/removed/` holds four tiny sources that use APIs removed or newly deprecated between 17 and 25; they are compiled with both JDKs.

```bash
export JDK17=/path/to/jdk-17 JDK25=/path/to/jdk-25
./scripts/run-all.sh      # regenerates output/
```

| Output | Shows |
|---|---|
| `01-runtime-behaviour.txt` | Security Manager, `Thread.stop`, default charset, `finalize`, `Unsafe` on both runtimes |
| `02-startup-flags.txt` | Which 17-era JVM options still start on 25 |
| `03-compile-removed-apis.txt` | What `javac` says about four APIs on each JDK |
| `04-jdeps-jdeprscan.txt` | The scanners run with JDK 25 tools against the JDK 17-built jar |
| `05-gc-defaults.txt` | Default collector and heap ergonomics with no flags |
| `06-legacy-stack-on-25.txt` | `mvn test` on JDK 25 for four generations of one Spring app (from `spring-boot-demo/openrewrite`) |
| `07-framework-minimums.txt` | Vendor documentation quotes (not produced by running code) |