RFR: 8340133: Investigate if the java launcher could give hints about JShell [v4]
Jan Lahoda
jlahoda at openjdk.org
Mon Oct 21 09:41:50 UTC 2024
> Currently, running `java` without any parameters will lead to an output that is a full `--help`, which is over 100 lines (on my computer at least), and it feels overwhelming. And many people might actually want to run JShell/REPL, not the `java` launcher, but it is difficult find out about JShell.
>
> The proposal herein is to print a much shorter help, together with a pointer to JShell, when the launcher does not know what to do. I.e. there is nothing specified to start, and no option like `--help` is specified. In particular, on my machine, it prints:
>
> $ java
> openjdk 24-internal 2025-03-18
>
> Usage: java [java options...] <application> [application arguments...]
>
> Where <application> is one of:
> <MainClass> to execute the main method of a compiled class
> -jar <JarFile>.jar to execute the main class of a JAR archive
> -m <module>[/<MainClass>] to execute the main class of a module
> <SourceFile>.java to compile and execute a single-file program
>
> Where key java options include:
> --class-path <class path>
> a ":"-separated list of directories and JAR archives to search for class files
> --module-path <module path>
> a ":"-separated list of directories and JAR archives to search for modules
>
> For more details about this launcher: java --help
> For an interactive Java environment: jshell
>
>
> Hopefully, this may be easier both for people trying to run something, and for people that are really looking for JShell.
>
> What do you think?
>
> Thanks!
Jan Lahoda has updated the pull request incrementally with two additional commits since the last revision:
- Using lowercase for the keys in the help, using 'source-file' program instead of 'single-file' program.
- Using an enum instead of booleans, as suggested.
-------------
Changes:
- all: https://git.openjdk.org/jdk/pull/21411/files
- new: https://git.openjdk.org/jdk/pull/21411/files/1791840b..5d82312f
Webrevs:
- full: https://webrevs.openjdk.org/?repo=jdk&pr=21411&range=03
- incr: https://webrevs.openjdk.org/?repo=jdk&pr=21411&range=02-03
Stats: 76 lines in 2 files changed: 14 ins; 2 del; 60 mod
Patch: https://git.openjdk.org/jdk/pull/21411.diff
Fetch: git fetch https://git.openjdk.org/jdk.git pull/21411/head:pull/21411
PR: https://git.openjdk.org/jdk/pull/21411
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