RFR: JDK-8306112 Implementation of JEP 445: Flexible Main Methods and Anonymous Main Classes (Preview) [v2]

[Alan Bateman]

On Thu, 27 Apr 2023 13:17:58 GMT, Jim Laskey <jlaskey at openjdk.org> wrote:

>> Add flexible main methods and anonymous main classes to the Java language.
>
> Jim Laskey has updated the pull request incrementally with one additional commit since the last revision:
> 
>   PreviewFeatures.isEnabled()

src/java.base/share/classes/sun/launcher/LauncherHelper.java line 45:

> 43: import java.lang.invoke.MethodHandles;
> 44: import java.lang.invoke.MethodHandles.Lookup;
> 45: import java.lang.invoke.MethodType;

Left over from an earlier version?

src/java.base/share/classes/sun/launcher/resources/launcher.properties line 240:

> 238:      Caused by: {1}: {2}
> 239: java.launcher.cls.error8=\
> 240:     Error: no non-private no argument constructor found in class {0}

Since this feature is for new developers then the error messages will need to be understand, maybe it should be "zero argument" and give an example to help.

src/java.base/share/native/libjli/java.c line 590:

> 588:         CHECK_EXCEPTION_NULL_LEAVE(mainID);
> 589:         (*env)->CallVoidMethod(env, mainObject, mainID);
> 590:         break;

This calls into LauncherHelper to get the "main type", then calls the static or new/instance method. I'm wondering if you tried have a single entry point in LauncherHelper instead. I think the only downside might be that the trampoline would show up in stack traces but @Hidden could hide that.

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PR Review Comment: https://git.openjdk.org/jdk/pull/13689#discussion_r1179174808
PR Review Comment: https://git.openjdk.org/jdk/pull/13689#discussion_r1179183719
PR Review Comment: https://git.openjdk.org/jdk/pull/13689#discussion_r1179172679