feature.md

Feature: Advanced OOP with Interfaces, Abstract Classes, and Collections

Description: The system should enable practicing advanced OOP concepts by defining interfaces, implementing abstract classes, and managing collections with ArrayList and HashMap. Students will build examples where they apply contracts through interfaces, enforce rules via abstract classes, store and retrieve data using collections, and simulate behaviors similar to data repositories. These activities prepare the foundation for working with databases and JDBC.

Acceptance Criteria:

• Scenario: Implement an interface Given an interface with defined methods When I implement it in multiple classes Then I can store the objects in an ArrayList and invoke their methods through the interface type.

• Scenario: Use an abstract class with polymorphism Given an abstract class with an abstract method When I extend it in different subclasses Then each subclass provides its own implementation and the method works polymorphically when called in a collection.

• Scenario: Manage a catalog with ArrayList Given a list of custom objects When I add, remove, or update elements Then the changes are reflected when I iterate and print the list.

• Scenario: Store and retrieve with HashMap Given a HashMap with key-value pairs When I add elements and search by key Then I can retrieve, update, or delete the correct values.

• Scenario: Simulate a repository in memory Given an interface defining CRUD-like operations When I implement it with a HashMap for storage Then I can save objects, find them by ID, delete them, and list all of them through the repository.

review-2.md

Activity 1 – Basic interface

1. Create an interface Operable with void start() and void stop().
2. Implement Operable in Engine and Fan.
3. In main, store both in an ArrayList<Operable> and loop through calling start() and stop().

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Activity 2 – Interface with return value

1. Create an interface Calculable with double calculate(double a, double b).
2. Implement Addition and Multiplication.
3. In main, use an ArrayList<Calculable> and run calculate(3,4) for each implementation.

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Activity 3 – Abstract + polymorphism

1. Create abstract class Shape with abstract double area().
2. Create Square(side) and Circle(radius) extending Shape.
3. In main, put 3–4 shapes into an ArrayList<Shape> and print each area().

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Activity 4 – Abstract with template

1. Create abstract class Process with final void execute() that calls prepare(), process(), finish().
2. Declare abstract void prepare() and process(), and a concrete finish() that prints “OK”.
3. Implement CsvProcess and JsonProcess. Test execute() for both.

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Activity 5 – Catalog with ArrayList

1. Create Product(id:String, name:String, price:double).
2. In main, use an ArrayList<Product>: add 5, remove 1 by index, update the name of the first.
3. Loop and print id - name - price.

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Activity 6 – Index with HashMap

1. Given an ArrayList<String> words, build a HashMap<String,Integer> with frequencies.
2. Print the keys and their counts.
3. If a word appears more than 2 times, mark it with “*” when printing.

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Activity 7 – Interface + HashMap

1. Create interface Storable { String key(); }.
2. Create User(id:String, name:String) implementing Storable (key = id).
3. In main, store users in a HashMap<String, User> using u.key().
4. Find, update the name by id, and remove a user.

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Activity 8 – Abstract + filter with ArrayList

1. abstract class Document { String title; abstract int pages(); }
2. Book(title, pages) and Magazine(title, pagesPerEdition).
3. In main, an ArrayList<Document> and print only those with pages() ≥ 100.

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Activity 9 – Strategies (interface)

1. interface Formatter { String format(String s); }
2. Implement UpperCase, LowerCase, TitleCase (capitalize first letter of each word).
3. In main, use an ArrayList<Formatter> and apply each strategy to the same string.

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Activity 10 – Simple router with HashMap

1. HashMap<String, Runnable> mapping "/home", "/about", "/contact" to Runnables that print messages.
2. In main, simulate 3 “requests” by looking up the key and running the Runnable.
3. If the route doesn’t exist, print “404”.

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Activity 11 – Mixed workshop (abstract + interface + collections)

1. abstract class Employee { String id; String name; abstract double monthlySalary(); }
2. interface Bonusable { double bonus(); }
3. Create FullTimeEmployee(baseSalary) implementing Bonusable (10% bonus).
4. Create HourlyEmployee(hours, rate) without bonus.
5. In main, ArrayList<Employee> with several; calculate total salaries and add bonus if applicable.
6. Print the total.

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Activity 12 – Bilingual dictionary (HashMap<String, ArrayList>)

1. HashMap<String, ArrayList<String>> dictionary (key = Spanish word, value = list of translations).
2. Add 3 words with 2–3 translations each.
3. Add a new translation to an existing word.
4. Print all words and their translations in format word: t1, t2, t3.

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Activity 13 – In-memory repository (interface + HashMap)

1. interface Repo<T> { void save(T t); T findById(String id); void delete(String id); }
2. class Student { String id; String name; }
3. class StudentRepo implements Repo<Student> using HashMap<String, Student>.
4. In main, save 3 students, get 1 by id, delete 1, and list the rest.

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Activity 14 – Basic filtering and sorting with ArrayList

1. Create Task(id, title, priority:int).
2. In main, ArrayList<Task> with 6 tasks (different priorities).
3. Filter tasks with priority ≥ 3 into a new list.
4. Sort the new list by ascending priority and print it.

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Activity 15 – Abstract with validation

1. abstract class Account { String number; double balance; abstract boolean withdraw(double amount); }
2. SavingsAccount (cannot go below 0).
3. CreditAccount (can go negative up to -1000).
4. In main, ArrayList<Account> and test valid/invalid withdrawals.