review comments for JEP 12: Preview Language and VM Features JDK-8195734 (original) (raw)

Alex Buckley alex.buckley at oracle.com
Mon Dec 10 20:41:44 UTC 2018

On 12/10/2018 12:26 PM, Harold David Seigel wrote:

On 12/10/2018 3:00 PM, Alex Buckley wrote:

3. The wording of the logging output is "Loading preview feature type $NAME". That sounds like the type is part of the preview feature, i.e., involved in supporting the preview feature, e.g., the java.lang.AutoCloseable type if the try-with-resources statement had been a preview feature. The word "type" also seems unusually abstract for logging output. Recommend "Loading class file that depends on preview features: $NAME", or, if it's redundant to say "Loading class file" in a log about class loading, then "$NAME depends on preview features of Java SE $RELEASETHATCORRESPONDSTOMAJORVERSION" We don't know if the class file actually depends on the preview features, just that it was compiled with 65535. So, how about: "Loading class file that is enabled for preview features: $NAME" ?

Per JEP 12, "A class file denotes that it depends on the preview VM features of Java SE $N by having a major_version item that corresponds to Java SE $N and a minor_version item that has all 16 bits set." What's actually in the code array is immaterial.

We already speak of enabling preview features in the Java compiler / JVM implementation, so it would be confusing to have an individual class file that "enabled" anything. (Would the file auto-enable the preview features of the compiler/runtime even if --enable-preview hadn't been passed?)

That said, it would be useful to draw attention to the class file version: "Class $NAME depends on preview features (class file version $MAJOR_VERSION.65535)"

Alex

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