JEP proposed to target JDK 11: 330: Launch Single-File Source-Code Programs

[Stuart Monteith]

While we are talking about platform specifics, I notice nobody has
mentioned binfmt_misc. If you are running on a suitably configured
Linux system you could just type:

echo ":java:E::java::<your JAVA_HOME>/bin/java:"
>/proc/sys/fs/binfmt_misc/register

That will allow you to run:
   $ ./HelloWorld.java

without modify the source at all.
Using binfmt_misc to handle "//! " at the beginning is possible with
some magic bytes and a wrapper are also possible if you want to avoid
needing the .java extension.
Most Debian installations will have an entry for "jar" files already.

While there probably isn't a scheme that would allow a single .java
file to run from the command line (or icon) on every platform, there
are perhaps platform specific means on most platforms.


BR,
   Stuart




On 24 May 2018 at 08:23, Robert Zenz <robert.zenz at sibvisions.com> wrote:
> I'm sorry, I still don't get why the shebang line is required at all for this
> proposal. I might argue that shebang lines are system dependent features and are
> typically only used with languages which treat `#` as a comment which is not the
> case in Java. Additionally, we can already "emulate" shebangs in Java (or any C
> like language) source files using a polyglot. Which is fore sure not that easy
> to understand, but it still gets the job done.
>
> I know what you're trying to do, but I fail to see how the achieved goal (of
> easily executing a Java source file by doing `./HelloWorld.java` versus `java
> HelloWorld.java`) validates the added special case just to support the shebang
> line (including possible confusion of newcomers why the first line is allowed to
> start with `#` but everywhere else is a syntax error).
>
> On 23.05.2018 23:01, Jonathan Gibbons wrote:
>> On 5/17/18 1:12 PM, mark.reinhold at oracle.com wrote:
>>
>>> The following JEP is proposed to target JDK 11:
>>>
>>>    330: Launch Single-File Source-Code Programs
>>>         http://openjdk.java.net/jeps/330
>>>
>>> Feedback on this proposal is more than welcome, as are reasoned
>>> objections.  If no such objections are raised by 23:00 UTC on Thursday,
>>> 24 May, or if they're raised and then satisfactorily answered, then
>>> per the JEP 2.0 process proposal [1] I'll target this JEP to JDK 11.
>>>
>>> - Mark
>>>
>>>
>>> [1] http://cr.openjdk.java.net/~mr/jep/jep-2.0-02.html
>> A number of points have been raised, regarding the interaction with javac and
>> shebang scripts.
>>
>> It was never a goal to modify javac to support shebang-java scripts. This can be
>> seen indirectly in the JEP in the description of how the first line may be
>> removed before passing the rest of the file as a normal CompilationUnit to the
>> compiler. With hindsight, this deserves to be stated as an explicit Non-Goal.
>>
>> There are various reasons to not want to change JLS or javac:
>>
>> 1. Changing JLS is a Big Deal, and comes with its own costs and constraints.
>> Further, shebang files are a platform-specific feature, and are not even defined
>> in the POSIX standard. The feature does not warrant changing a JCP-controlled
>> specification.
>>
>> 2. Changing javac to accept shebang-java files is also a Big Deal. Modifying the
>> command-line options to accept files that do not follow the standard naming
>> conventions would introduce complexity and potential ambiguity.
>>
>> 3. There is no compelling need to change JLS or javac.  As demonstrated by the
>> proposed implementation, no change to JLS or javac is actually necessary in
>> order to implement the feature. It is therefore at most a convenience if javac
>> were to be adapted to ignore shebang lines.
>>
>> Shebang scripts are an executable format defined on some, but not all,
>> platforms. Creating a shebang script is typically more than just adding an
>> initial first line to a file; it typically involves a number of steps:
>>
>> a. Add an initial shebang line to the file
>> b. Rename the file to a "command-friendly" name
>> c. Make the file executable
>> d. Install the file in some standard location
>>
>> While renaming the file to a command-friendly name is optional, it is also
>> expected to be common practice. For example, a source file named
>> `HelloWorld.java` might be installed as `helloworld`. And, while the JEP
>> describes use cases for executing a small single-file program with `java
>> HelloWorld.java` or executing it as a platform-specific shebang script with just
>> `helloworld`, it does not seem like there is a common use case to execute
>> `HelloWorld.java`. So, if the shebang script is typically renamed to a
>> command-friendly name, it will not be possible to compile it directly, with
>> "javac helloworld", because that is not a valid command line for javac. This
>> reduces any potential convenience of having javac ignore shebang lines.
>>
>> Since Java source files are different artifacts to platform-specific executable
>> scripts, it makes sense to treat them differently, and since we do not want to
>> change the Java language to support shebang lines, the suggestion is to amend
>> the JEP and implementation so that shebang lines are never stripped from Java
>> source files, i.e. files ending in `.java`. This avoids the problem of having
>> the ecosystem of tools handling Java source files having to deal with arbitrary
>> artifacts like shebang lines.  The change would still permit the direct
>> execution of Java source files, such as `java HelloWorld.java`, and the
>> execution of shebang scripts, such as `helloworld`.
>>
>>  -- Jon