openjdk:17-alpine3.14 image cannot compile sealed classes ("sealed classes are a preview feature")

It's not a big issue, but someone might have this problem sooner or later and maybe it's good that it was to be found somewhere in the Internet.

I've recently tried to compile my JDK17 project with openjdk:17-alpine3.14 docker image.

To my surprise, it wouldn't compile sealed classes, which were released as a feature (not preview feature) in JDK 17.

Running the following command:

docker run --rm -v $PWD:/tmp/src -w /tmp/src openjdk:17-alpine3.14 ./mvnw clean install

ended with this error:

[INFO] Compiling 1 source file to /tmp/src/target/classes
[INFO] -------------------------------------------------------------
[ERROR] COMPILATION ERROR :
[INFO] -------------------------------------------------------------
[ERROR] /tmp/src/src/main/java/com/tp/samples/openjdk17sealedclass/DoesNotCompileSample.java:[5,12] sealed classes are a preview feature and are disabled by default.
  (use --enable-preview to enable sealed classes)
[INFO] 1 error
[INFO] -------------------------------------------------------------
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  13.553 s
[INFO] Finished at: 2022-12-13T21:57:41Z
[INFO] ------------------------------------------------------------------------

I created a minimal reproducible project here: openjdk:17-alpine3.14 sealed classes error.

It's not a big deal, because I wouldn't use such image bare bones in production. It's just a minor inconvenience. I know this particular image might not be even maintained anymore and do not expect any fix. Just wanted to leave this issue for potential unfortunate souls who'd stumble upon the same error in the future.

Cheers

docker-library / openjdk

openjdk:17-alpine3.14 image cannot compile sealed classes ("sealed classes are a preview feature") #521