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I don't know much about that, but if you search this forum you will probably find that the Java21 certificaiton exam is not yet available, nor is its syllabus. So we don't yet know what will be in the exam, and it is impossible to complete the book without knowing that. The
authors' website shows that book as “coming soon,” and
Amazon says it is available for pre‑order and will be available on 24th December 2024.