Building processing throws `UnsupportedClassVersionError` in `:core:examples:Basic.main()`

[clankill3r]

I try to build processing with a clean clone of the repository.

Following the build instructions:
https://github.com/processing/processing4/blob/main/BUILD.md

1

The run button doesn't work in IntelliJ:

13:23:05: Executing ':core:examples:Basic.main()'…

Task :plugins:library:checkKotlinGradlePluginConfigurationErrors SKIPPED
Task :plugins:library:compileKotlin UP-TO-DATE
Task :plugins:library:compileJava NO-SOURCE
Task :plugins:library:pluginDescriptors UP-TO-DATE
Task :plugins:library:processResources UP-TO-DATE
Task :plugins:library:classes UP-TO-DATE
Task :plugins:library:jar UP-TO-DATE
Task :core:checkKotlinGradlePluginConfigurationErrors SKIPPED
Task :core:compileKotlin NO-SOURCE

Task :core:compileJava
Note: Some input files use or override a deprecated API.
Note: Recompile with -Xlint:deprecation for details.

Task :core:processResources
Task :core:classes
Task :core:jar

Task :core:examples:compileJava

Task :core:examples:processResources NO-SOURCE
Task :core:examples:classes
Note: /Users/doeke/Documents/processing4-w_branches/core/examples/src/main/java/Basic.java uses or overrides a deprecated API.
Note: Recompile with -Xlint:deprecation for details.

Task :core:examples:Basic.main() FAILED
[Incubating] Problems report is available at: file:///Users/doeke/Documents/processing4-w_branches/.build/reports/problems/problems-report.html
9 actionable tasks: 5 executed, 4 up-to-date
Error: LinkageError occurred while loading main class Basic
java.lang.UnsupportedClassVersionError: Basic has been compiled by a more recent version of the Java Runtime (class file version 65.0), this version of the Java Runtime only recognizes class file versions up to 61.0

FAILURE: Build failed with an exception.

• What went wrong:
  Execution failed for task ':core:examples:Basic.main()'.

Process 'command '/Library/Java/JavaVirtualMachines/temurin-17.jdk/Contents/Home/bin/java'' finished with non-zero exit value 1

• Try:

Run with --stacktrace option to get the stack trace.
Run with --info or --debug option to get more log output.
Run with --scan to get full insights.
Get more help at https://help.gradle.org.

BUILD FAILED in 2s
13:23:08: Execution finished ':core:examples:Basic.main()'.

Which is triggered by: Runtime.getRuntime().exec("echo Hello World");

If I comment out those lines then I get:

17:06:15: Executing ':core:examples:Basic.main()'…

Task :plugins:library:checkKotlinGradlePluginConfigurationErrors SKIPPED
Task :plugins:library:compileKotlin UP-TO-DATE
Task :plugins:library:compileJava NO-SOURCE
Task :plugins:library:pluginDescriptors UP-TO-DATE
Task :plugins:library:processResources UP-TO-DATE
Task :plugins:library:classes UP-TO-DATE
Task :plugins:library:jar UP-TO-DATE
Task :core:checkKotlinGradlePluginConfigurationErrors SKIPPED
Task :core:compileKotlin NO-SOURCE
Task :core:compileJava UP-TO-DATE
Task :core:processResources UP-TO-DATE
Task :core:classes UP-TO-DATE
Task :core:jar UP-TO-DATE
Task :core:examples:compileJava
Task :core:examples:processResources NO-SOURCE
Task :core:examples:classes

Task :core:examples:Basic.main() FAILED
9 actionable tasks: 2 executed, 7 up-to-date
Error: LinkageError occurred while loading main class Basic
java.lang.UnsupportedClassVersionError: Basic has been compiled by a more recent version of the Java Runtime (class file version 65.0), this version of the Java Runtime only recognizes class file versions up to 61.0

FAILURE: Build failed with an exception.

• What went wrong:
  Execution failed for task ':core:examples:Basic.main()'.

Process 'command '/Library/Java/JavaVirtualMachines/temurin-17.jdk/Contents/Home/bin/java'' finished with non-zero exit value 1

• Try:

Run with --stacktrace option to get the stack trace.
Run with --info or --debug option to get more log output.
Run with --scan to get full insights.
Get more help at https://help.gradle.org.

BUILD FAILED in 872ms
17:06:16: Execution finished ':core:examples:Basic.main()'.

And so on...
Also if I check the module settings in IntelliJ then they default to 21 for me.
Upon checking the gradle files I see nowhere something among the lines of:

languageVersion = JavaLanguageVersion.of(17)

It seems like whoever made processing move away from maven to gradle had only JDK 17 installed.
I don't want to dig deeper cause I simply don't have the time but it would be nice if some housekeeping would take place.

[SableRaf]

Hi @clankill3r and thanks for reporting this.

Quick question: did you follow step 6 of the IntelliJ instructions in BUILD.md?

The build currently assumes Java 17, and BUILD.md calls this out explicitly.

Please check both of these:

• Project SDK:
  File > Project Structure > Project > SDK → set this to JDK 17 (not 21)

• Gradle JVM:
  File > Settings > Build Tools > Gradle > Gradle JVM → also set this to JDK 17

Once both are set, reimport the Gradle project and try running the example again.

---

Also , just a small ask: please keep comments focused on the technical issue.

I can see the frustration here. Build issues are annoying. However, phrases like

It seems like whoever made processing move away from maven to gradle had only JDK 17 installed.
I don't want to dig deeper cause I simply don't have the time but it would be nice if some housekeeping would take place.

can come across as dismissive, and do not fit the atmosphere we’re trying to create for the project.

I'm genuinely glad you’re here and taking the time to report issues, and we will all appreciate your help in keeping discussions constructive and welcoming. We’re all doing our best here 💙

[Stefterv]

Unsupported class error sounds to me that you compiled the project before with a different JDK.
Try

./gradlew clean

@SableRaf maybe a good idea to add that as a potential troubleshooting step

[SableRaf]

Thanks @Stefterv! I created a PR to add this troubleshooting step in BUILD.md: #1430