Summary

Improve the Java source launcher to imply --source N when only --enable-preview is given on the command-line using Java N.

Problem

Primary user of the Java source launcher is an early stage programmer learning Java. Explicit requirement of --enable-preview followed by --source N arguments to enable preview features is an obstacle for novice Java source launcher users.

Solution

Improve the Java source launcher to use preview features more easy by letting --enable-preview imply --source N, with N automatically selected for current Java Runtime.

Specification

The man page of the java launcher will be extended with a new item in the In source-file mode, compilation proceeds as follows subsection as follows:

- If `--enable-preview` is specified, the `--source N` arguments can be omitted.
  The Java Runtime of version `N` implies an implicit `--release N` being added
  for the compilation of the source files.

An update of the related command-line help message of java is not required, because the current text covers the new behaviour already:

    --enable-preview
                  allow classes to depend on preview features of this release