Creation BookManager Class

Do not invent a full library system from the class name. Ask what BookManager owns: a catalog, borrowing, inventory, search, or all of them; then define a narrow interface. A reasonable baseline has a Book entity with stable ID, title, authors, and metadata, plus a manager indexed by ID and perhaps normalized title/author search keys. Make create validate required fields and uniqueness, make updates explicit about allowed fields, and return domain errors rather than silent nulls. If multiple callers can mutate inventory, use a version or transactional repository boundary rather than an unsynchronized map. Separate the manager's business rules from persistence so an in-memory implementation can be replaced. Basic ID lookup is expected O(1); indexed search and persistence costs depend on the chosen requirements.