Mình cũng thực hiện thử thách này và đã đưa code lên Github: duykhanh472/luyentayjava.
Về cơ bản là: Dùng Scanner rồi lấy kiểu như cái *098# của Viettel ấy, nhập số 1, 2, 3 rồi Option này kia. Mọi thứ đều là CLI và hãy dành phần lớn thời gian của bản thân để nghĩ về logic của code chứ không phải là nên làm giao diện bằng JavaFX hay Swing hay gì.
Scanner for input. Support +, -, *, / in a loop. Ask for numbers and operator, show result, repeat until user quits.ArrayList<String> for tasks. Menu: add task, list tasks, remove task, save to file, load from file. Use basic file I/O.Account class with balance. Methods: deposit, withdraw, show balance. Use ArrayList<Account> to manage multiple accounts.Student class (name, list of grades). Methods: add grade, calculate average, show grades. Use ArrayList<Student> for all students.Book class (title, author, year, isBorrowed). Use ArrayList<Book>. Menu: add book, list all books, borrow book, return book, search by title/author.Item class (id, name, quantity, price). Use ArrayList<Item>. Menu: add item, list items, update quantity, remove item, show total value.Contact class (name, phone, email). Use HashMap<String, Contact> (name as key). Menu: add contact, search by name, list all, delete contact, update contact.Expense class (date, amount, category, description). Use ArrayList<Expense>. Menu: add expense, list all, show by category, total expenses, monthly summary.Recipe class (name, list of ingredients, instructions). Use ArrayList<Recipe>. Menu: add recipe, list all recipes, search by name/ingredient, view recipe details.Scanner or Files. Count total words, unique words (use HashSet), and word frequency (HashMap). Display results.char array or StringBuilder for hidden word. Loop: guess letter, update display, track wrong guesses. End on win or lose.StringBuilder. Allow multiple generations.Movie class (title, director, year, genre). Use ArrayList<Movie>. Menu: add movie, list all, search by title/genre, remove movie.Account class (accountNumber, pin, balance). Menu: login, check balance, deposit, withdraw, exit. Handle insufficient funds.Task class (description, priority, dueDate). Use ArrayList<Task>. Menu: add task, list tasks (sorted by priority/due date), mark complete, remove task.Vehicle class (licensePlate, model, rentalPrice). Inherit Car, Bike, and Truck with extra fields. Use ArrayList<Vehicle>. Menu: add vehicle, list available, rent, return.Animal class (name, age) with makeSound() method. Inherit different animals overriding makeSound(). Use ArrayList<Animal>. Menu: add animal, list all, make all sounds.Item class (name, price, quantity). Create Cart class with ArrayList<Item>. Menu: add item, remove item, list cart, calculate total.HashMap<String, String> (word → definition). Menu: add word, search word, list all words, delete word, update definition.Question base class, inherit MultipleChoice and TrueFalse. Use ArrayList<Question>. Ask questions, track score, show final result.HashMap for error type frequency. Display summary.Pair<T, U> class with two values. Use it to store different data types (e.g. name-age, product-price).Stack<T> class using ArrayList. Methods: push, pop, peek, isEmpty, size. Test with different types.Queue<T> class using ArrayList. Methods: enqueue, dequeue, peek, isEmpty, size. Test with different types.Student class, inherit Undergraduate and Graduate. Use ArrayList<Student>. Menu: add student, list all, show details, calculate averages.Room class and Player (with inventory ArrayList). Connect rooms. Menu: go direction, take item, look, inventory.Note class (title, content, timestamp). Use ArrayList<Note>. Menu: create note, list notes, view note, delete note, save/load from file.Transaction class (date, amount, category, type). Use ArrayList<Transaction>. Menu: add transaction, list all, summaries (total income/expense, by category) using streams.