JEP 445 support: Unnamed Classes and Instance Main Methods

[linux-china]

JEP 445 support for JBang.

Create Main.java Java file:

///usr/bin/env jbang "$0" "$@" ; exit $?
//JAVA 21
//JAVAC_OPTIONS --enable-preview -source 21
//JAVA_OPTIONS --enable-preview

void main(){
        System.out.println("Hello, World!");
}

Then run jbang run --verbose Main.java, and statcktrace as following:

[jbang] [0:286] jbang version 0.107.0
[jbang] [0:299] Resolving resource ref: Main.java
[jbang] [0:302] Resolved resource ref as: Main.java (cached as: /Users/linux_china/IdeaProjects/java21-in-action/Main.java)
[jbang] [0:359] Looking for JDK: 21
[jbang] [0:363] Using JDK: 21 (21, current, /Users/linux_china/.jbang/cache/jdks/21)
[jbang] [0:363] No build required. Reusing jar from /Users/linux_china/.jbang/cache/jars/Main.java.8f8f49b93db276e6a59a1b145e26592539e968c045885a1b51ea31d3959ca24d/Main.jar
[jbang] [0:365] Looking for JDK: 21
[jbang] [0:366] Using JDK: 21 (21, current, /Users/linux_china/.jbang/cache/jdks/21)
[jbang] [0:366] Looking for JDK: 21
[jbang] [0:366] Using JDK: 21 (21, current, /Users/linux_china/.jbang/cache/jdks/21)
[jbang] [0:368] [ERROR] no main class deduced, specified nor found in a manifest
dev.jbang.cli.ExitException: no main class deduced, specified nor found in a manifest
	at dev.jbang.source.generators.JarCmdGenerator.generateCommandLineList(JarCmdGenerator.java:168)
	at dev.jbang.source.generators.BaseCmdGenerator.generate(BaseCmdGenerator.java:56)
	at dev.jbang.cli.Run.doCall(Run.java:99)
	at dev.jbang.cli.BaseCommand.call(BaseCommand.java:145)
	at dev.jbang.cli.BaseCommand.call(BaseCommand.java:21)
	at picocli.CommandLine.executeUserObject(CommandLine.java:1953)
	at picocli.CommandLine.access$1300(CommandLine.java:145)
	at picocli.CommandLine$RunLast.executeUserObjectOfLastSubcommandWithSameParent(CommandLine.java:2358)
	at picocli.CommandLine$RunLast.handle(CommandLine.java:2352)
	at dev.jbang.cli.JBang$3.handle(JBang.java:148)
	at dev.jbang.cli.JBang$3.handle(JBang.java:143)
	at picocli.CommandLine$AbstractParseResultHandler.execute(CommandLine.java:2179)
	at picocli.CommandLine$RunLast.execute(CommandLine.java:2316)
	at picocli.CommandLine.execute(CommandLine.java:2078)
	at dev.jbang.Main.main(Main.java:14)
[jbang] [0:368] If you believe this a bug in jbang, open an issue at https://github.com/jbangdev/jbang/issues

You can run it with jbang run --verbose -m Main Main.java, and it works well.

JEP 445 has been implemented on openjdk/jdk@98b53c0, and next version of JDK 21 will include this feature.

[maxandersen]

Is there a build one can download and try ?

We really just need to detect the new method generated and could then remove need for manual main.

[maxandersen]

managed to build a jdk - I can't get -m Main to work.

[maxandersen]

sorry - it does work - had typo.

[linux-china]

JDK 21 build 26 implemented JEP 445 already. https://jdk.java.net/21/

[maxandersen]

Done in 0.108