RFR: 8340133: Add concise usage message to the java executable [v7]

[Magnus Ihse Bursie]

On Mon, 11 Nov 2024 08:13:18 GMT, Jan Lahoda <jlahoda at openjdk.org> wrote:

>> 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` executable, 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 executable 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:
>> 
>> 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 source-file program
>> 
>> Where key java options include:
>>   --class-path <class path>
>>     where <class path> is a list of directories and JAR archives to search for class files, separated by ":"
>>   --module-path <module path>
>>     where <module path> is a list of directories and JAR archives to search for modules, separated by ":"
>> 
>> For additional help on usage:           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 with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 11 additional commits since the last revision:
> 
>  - Merge branch 'master' into JDK-8340133-2
>  - Using correct pplaceholders.
>  - Adjusting text as suggested.
>  - Cleaning up the concise message:
>    - using 2 spaces instead of 4,
>    - rewording the "for more use --help" part of the message as suggested to avoid the word "launcher".
>  - 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.
>  - Adjusting the concise help as suggested: 'using main class of a JAR archive' and '<JarFile>.jar'/'<SourceFile>.java'
>  - Adjusting the concise help based on review suggestions.
>  - Cleanup.
>  - Adjusting/improving the concise help.
>  - ... and 1 more: https://git.openjdk.org/jdk/compare/99abd24b...b4d7b493

Marked as reviewed by ihse (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/21411#pullrequestreview-2426961678