Serena

/// Data models for the test application library models; /// Represents a user in the system class User { /// User's unique identifier final int id; /// User's name final String name; /// User's email address final String email; /// User's age int _age; /// Constructor for creating a User User(this.id, this.name, this.email, this._age); /// Named constructor for creating a user with default values User.withDefaults(this.id, this.name) : email = '$name@example.com', _age = 0; /// Getter for user's age int get age => _age; /// Setter for user's age with validation set age(int value) { if (value < 0 || value > 150) { throw ArgumentError('Age must be between 0 and 150'); } _age = value; } /// Checks if the user is an adult bool get isAdult => _age >= 18; /// Returns a string representation of the user @override String toString() { return 'User(id: $id, name: $name, email: $email, age: $_age)'; } /// Checks equality based on user ID @override bool operator ==(Object other) { if (identical(this, other)) return true; return other is User && other.id == id; } @override int get hashCode => id.hashCode; } /// Represents a product in an e-commerce system class Product { final String id; final String name; final double price; final String category; int _stock; Product(this.id, this.name, this.price, this.category, this._stock); /// Getter for current stock int get stock => _stock; /// Reduces stock by the specified amount bool reduceStock(int amount) { if (amount <= 0) { throw ArgumentError('Amount must be positive'); } if (_stock >= amount) { _stock -= amount; return true; } return false; } /// Increases stock by the specified amount void increaseStock(int amount) { if (amount <= 0) { throw ArgumentError('Amount must be positive'); } _stock += amount; } /// Checks if the product is in stock bool get isInStock => _stock > 0; /// Calculates the total value of stock double get totalStockValue => _stock * price; } /// An abstract base class for different types of accounts abstract class Account { final String accountNumber; double _balance; Account(this.accountNumber, this._balance); double get balance => _balance; /// Abstract method that must be implemented by subclasses bool withdraw(double amount); /// Deposits money into the account void deposit(double amount) { if (amount <= 0) { throw ArgumentError('Deposit amount must be positive'); } _balance += amount; } } /// A savings account implementation class SavingsAccount extends Account { final double interestRate; SavingsAccount(super.accountNumber, super.balance, this.interestRate); @override bool withdraw(double amount) { if (amount <= 0) { throw ArgumentError('Withdrawal amount must be positive'); } if (_balance >= amount) { _balance -= amount; return true; } return false; } /// Applies interest to the account balance void applyInterest() { _balance += _balance * interestRate / 100; } } /// Generic container class demonstrating type parameters class Container<T> { final List<T> _items = []; /// Adds an item to the container void add(T item) { _items.add(item); } /// Removes an item from the container bool remove(T item) { return _items.remove(item); } /// Gets all items in the container List<T> get items => List.unmodifiable(_items); /// Gets the number of items int get length => _items.length; /// Checks if the container is empty bool get isEmpty => _items.isEmpty; /// Finds the first item matching the predicate T? find(bool Function(T) predicate) { for (final item in _items) { if (predicate(item)) { return item; } } return null; } }