Updated free-programming-books-langs.md (Java 23 key concepts in brief e-book) (#11327)

* Updated free-programming-books-langs.md

* Update URL

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Co-authored-by: Sergey Nechaev <support@detasked.com>

books/free-programming-books-langs.md

@@ -1057,6 +1057,7 @@ Books on general-purpose programming that don't focus on a specific language are
 * [Introduction to Programming in Java](http://introcs.cs.princeton.edu/java/home/) - Robert Sedgewick, Kevin Wayne
 * [Introduction to Programming Using Java](http://math.hws.edu/javanotes) - David J. Eck (HTML, PDF, ePUB + exercises)
 * [Introduction to Programming Using Java (5th Edition - final version, 2010 Jun)](https://math.hws.edu/eck/cs124/javanotes5) - David J. Eck (HTML, PDF, ePUB + exercises)
+* [Java 23 - Key Concepts in Brief](https://petrucci.dev/java23.html) - Sergio Petrucci (PDF)
 * [Java Application Development on Linux (2005)](https://ptgmedia.pearsoncmg.com/images/013143697X/downloads/013143697X_book.pdf) - Carl Albing, Michael Schwarz (PDF)
 * [Java, Java, Java Object-Oriented Problem Solving](https://archive.org/details/JavaJavaJavaObject-orientedProblemSolving/page/n0) - R. Morelli, R.Walde
 * [Java Language and Virtual Machine Specifications](https://docs.oracle.com/javase/specs/) - James Gosling, et al.