[Java] Improve how-to document/run Java cookbooks recipes

Currently Java cookbooks recipes are examples runnable on JShell environment and compare the results.

For this purpose JShell environment is needed.

The purpose of this ticket is to create new ways about how the same code could be run without JShell dependency:
- Current `testcode` is able to run inside `public static void main` method without problems, base on this one idea could be to add this line on the recipe to te user could copy all the lines and run that without to adding that contend inside a method, and delete that at runtime for JShell process
- Other options ...

Start by reviewing the Java cookbook recipes, the current `testcode`, and how recipes are run in the JShell environment. Compare the existing `public static void main` approach with the requested copy-and-run workflow, then clarify which alternative should be implemented. Done means users can run the same recipe code without a JShell dependency while preserving the result comparisons.

Written by the indexing model from the issue text.