100 Mini Java Exercises: Final Challenges -BOOK 12: Integrate OOP, Collections, Files, Validation, and Business Logic Step by

Ready to stop practicing Java one concept at a time and start solving problems that feel like real programming?100 Mini Java Exercises: Final Challenges is the twelfth and final volume in the 100 Mini Java Exercises series. Instead of introducing another isolated topic, this book brings together the skills developed throughout the collection and challenges you to decide which tools a problem actually needs.Across 100 progressive challenges, you will work with object-oriented programming, ArrayList and HashMap, validation, business rules, file persistence, searches, filters, statistics, related objects, transactions, error recovery, refactoring, and increasingly open-ended specifications.The difficulty grows through decision-making rather than through frameworks or advanced external technologies. Every challenge can be solved with standard Java and console applications, making the book ideal for students, self-taught programmers, and junior developers who want to strengthen their practical problem-solving skills.Each exercise includes a clear prompt, a working Java solution, a concise explanation, cases to test, and a possible extension so you can keep practicing beyond the proposed answer.By the end of the book, you will be more comfortable turning requirements into classes, choosing suitable collections, enforcing valid states, preserving data, connecting related objects, and breaking larger problems into smaller, manageable parts.You have learned the pieces. Now it is time to use them together.