{"title":"Exercise: Single Responsibility Principle","description":null,"content":"Try implementing the below code exercises to reinforce your understanding. Your goal is to implement the classes below so that they produce the expected output.\n\n---\n\n# Exercise 1: OrderService God Class\n\n\n**Problem:** You have an `OrderService` class that handles order processing, inventory management, and sending notifications. This class has three distinct responsibilities tangled together. Your task is to refactor it into three focused classes: `OrderProcessor`, `InventoryManager`, and `NotificationService`.\n\n**Requirements:**\n\n- `OrderProcessor` should handle order validation and total calculation\n- `InventoryManager` should handle stock checks and stock updates\n- `NotificationService` should handle sending order confirmation messages\n- Each class should accept dependencies through its constructor (or method parameters) rather than doing everything internally\n\n```java\nimport java.util.*;\n\n// Before: One class doing three unrelated jobs\nclass OrderService {\n private Map inventory = new HashMap<>();\n private List orders = new ArrayList<>();\n\n public OrderService() {\n inventory.put(\"LAPTOP\", 10);\n inventory.put(\"PHONE\", 25);\n inventory.put(\"TABLET\", 15);\n }\n\n public void placeOrder(String productId, int quantity, String customerEmail) {\n // Responsibility 1: Inventory check\n Integer stock = inventory.get(productId);\n if (stock == null || stock < quantity) {\n System.out.println(\"Insufficient stock for \" + productId);\n return;\n }\n\n // Responsibility 2: Order processing\n double pricePerUnit = 100.0; // Simplified pricing\n double total = pricePerUnit * quantity;\n String orderId = \"ORD-\" + (orders.size() + 1);\n orders.add(orderId);\n\n // Responsibility 3: Update inventory\n inventory.put(productId, stock - quantity);\n\n // Responsibility 4: Send notification\n System.out.println(\"Email to \" + customerEmail + \": Order \" + orderId\n + \" confirmed. Total: $\" + total);\n }\n}\n\n// TODO: Refactor into OrderProcessor, InventoryManager, and NotificationService.\n\npublic class Main {\n public static void main(String[] args) {\n // After refactoring, usage should look like:\n // InventoryManager inventory = new InventoryManager();\n // NotificationService notifications = new NotificationService();\n // OrderProcessor processor = new OrderProcessor(inventory, notifications);\n // processor.placeOrder(\"LAPTOP\", 2, \"alice@example.com\");\n }\n}\n```\n\n```python\n# Before: One class doing three unrelated jobs\nclass OrderService:\n def __init__(self):\n self.inventory = {\"LAPTOP\": 10, \"PHONE\": 25, \"TABLET\": 15}\n self.orders = []\n\n def place_order(self, product_id: str, quantity: int, customer_email: str):\n # Responsibility 1: Inventory check\n stock = self.inventory.get(product_id, 0)\n if stock < quantity:\n print(f\"Insufficient stock for {product_id}\")\n return\n\n # Responsibility 2: Order processing\n price_per_unit = 100.0\n total = price_per_unit * quantity\n order_id = f\"ORD-{len(self.orders) + 1}\"\n self.orders.append(order_id)\n\n # Responsibility 3: Update inventory\n self.inventory[product_id] = stock - quantity\n\n # Responsibility 4: Send notification\n print(f\"Email to {customer_email}: Order {order_id} confirmed. Total: ${total}\")\n\n# TODO: Refactor into OrderProcessor, InventoryManager, and NotificationService.\n\nif __name__ == \"__main__\":\n # After refactoring, usage should look like:\n # inventory = InventoryManager()\n # notifications = NotificationService()\n # processor = OrderProcessor(inventory, notifications)\n # processor.place_order(\"LAPTOP\", 2, \"alice@example.com\")\n pass\n```\n\n```cpp\n#include \n#include \n#include \n#include \n\nusing namespace std;\n\n// Before: One class doing three unrelated jobs\nclass OrderService {\nprivate:\n map inventory;\n vector orders;\n\npublic:\n OrderService() {\n inventory[\"LAPTOP\"] = 10;\n inventory[\"PHONE\"] = 25;\n inventory[\"TABLET\"] = 15;\n }\n\n void placeOrder(const string& productId, int quantity,\n const string& customerEmail) {\n // Responsibility 1: Inventory check\n auto it = inventory.find(productId);\n if (it == inventory.end() || it->second < quantity) {\n cout << \"Insufficient stock for \" << productId << endl;\n return;\n }\n\n // Responsibility 2: Order processing\n double pricePerUnit = 100.0;\n double total = pricePerUnit * quantity;\n string orderId = \"ORD-\" + to_string(orders.size() + 1);\n orders.push_back(orderId);\n\n // Responsibility 3: Update inventory\n it->second -= quantity;\n\n // Responsibility 4: Send notification\n cout << \"Email to \" << customerEmail << \": Order \" << orderId\n << \" confirmed. Total: $\" << total << endl;\n }\n};\n\n// TODO: Refactor into OrderProcessor, InventoryManager, and NotificationService.\n\nint main() {\n // After refactoring, usage should look like:\n // InventoryManager inventory;\n // NotificationService notifications;\n // OrderProcessor processor(inventory, notifications);\n // processor.placeOrder(\"LAPTOP\", 2, \"alice@example.com\");\n return 0;\n}\n```\n\n```go\npackage main\n\nimport \"fmt\"\n\n// Before: One class doing three unrelated jobs\ntype OrderService struct {\n\tinventory map[string]int\n\torders []string\n}\n\nfunc NewOrderService() *OrderService {\n\treturn &OrderService{\n\t\tinventory: map[string]int{\n\t\t\t\"LAPTOP\": 10,\n\t\t\t\"PHONE\": 25,\n\t\t\t\"TABLET\": 15,\n\t\t},\n\t\torders: []string{},\n\t}\n}\n\nfunc (s *OrderService) PlaceOrder(productId string, quantity int, customerEmail string) {\n\t// Responsibility 1: Inventory check\n\tstock, ok := s.inventory[productId]\n\tif !ok || stock < quantity {\n\t\tfmt.Println(\"Insufficient stock for \" + productId)\n\t\treturn\n\t}\n\n\t// Responsibility 2: Order processing\n\tpricePerUnit := 100.0\n\ttotal := pricePerUnit * float64(quantity)\n\torderId := fmt.Sprintf(\"ORD-%d\", len(s.orders)+1)\n\ts.orders = append(s.orders, orderId)\n\n\t// Responsibility 3: Update inventory\n\ts.inventory[productId] = stock - quantity\n\n\t// Responsibility 4: Send notification\n\tfmt.Printf(\"Email to %s: Order %s confirmed. Total: $%v\\n\", customerEmail, orderId, total)\n}\n\n// TODO: Refactor into OrderProcessor, InventoryManager, and NotificationService.\n\nfunc main() {\n\t// After refactoring, usage should look like:\n\t// inventory := NewInventoryManager()\n\t// notifications := NewNotificationService()\n\t// processor := NewOrderProcessor(inventory, notifications)\n\t// processor.PlaceOrder(\"LAPTOP\", 2, \"alice@example.com\")\n}\n```\n\n```csharp\nusing System;\nusing System.Collections.Generic;\n\n// Before: One class doing three unrelated jobs\nclass OrderService\n{\n private Dictionary inventory = new Dictionary();\n private List orders = new List();\n\n public OrderService()\n {\n inventory[\"LAPTOP\"] = 10;\n inventory[\"PHONE\"] = 25;\n inventory[\"TABLET\"] = 15;\n }\n\n public void PlaceOrder(string productId, int quantity, string customerEmail)\n {\n // Responsibility 1: Inventory check\n if (!inventory.ContainsKey(productId) || inventory[productId] < quantity)\n {\n Console.WriteLine(\"Insufficient stock for \" + productId);\n return;\n }\n\n // Responsibility 2: Order processing\n double pricePerUnit = 100.0;\n double total = pricePerUnit * quantity;\n string orderId = \"ORD-\" + (orders.Count + 1);\n orders.Add(orderId);\n\n // Responsibility 3: Update inventory\n inventory[productId] -= quantity;\n\n // Responsibility 4: Send notification\n Console.WriteLine($\"Email to {customerEmail}: Order {orderId} confirmed. Total: ${total}\");\n }\n}\n\n// TODO: Refactor into OrderProcessor, InventoryManager, and NotificationService.\n\nclass Program\n{\n static void Main()\n {\n // After refactoring, usage should look like:\n // var inventory = new InventoryManager();\n // var notifications = new NotificationService();\n // var processor = new OrderProcessor(inventory, notifications);\n // processor.PlaceOrder(\"LAPTOP\", 2, \"alice@example.com\");\n }\n}\n```\n\n```typescript\n// Before: One class doing three unrelated jobs\nclass OrderService {\n private inventory: Map = new Map([\n [\"LAPTOP\", 10],\n [\"PHONE\", 25],\n [\"TABLET\", 15],\n ]);\n private orders: string[] = [];\n\n placeOrder(productId: string, quantity: number, customerEmail: string): void {\n // Responsibility 1: Inventory check\n const stock = this.inventory.get(productId) ?? 0;\n if (stock < quantity) {\n console.log(`Insufficient stock for ${productId}`);\n return;\n }\n\n // Responsibility 2: Order processing\n const pricePerUnit = 100.0;\n const total = pricePerUnit * quantity;\n const orderId = `ORD-${this.orders.length + 1}`;\n this.orders.push(orderId);\n\n // Responsibility 3: Update inventory\n this.inventory.set(productId, stock - quantity);\n\n // Responsibility 4: Send notification\n console.log(`Email to ${customerEmail}: Order ${orderId} confirmed. Total: $${total}`);\n }\n}\n\n// TODO: Refactor into OrderProcessor, InventoryManager, and NotificationService.\n\n// After refactoring, usage should look like:\n// const inventory = new InventoryManager();\n// const notifications = new NotificationService();\n// const processor = new OrderProcessor(inventory, notifications);\n// processor.placeOrder(\"LAPTOP\", 2, \"alice@example.com\");\n```\n\n#### Solutions\n\n```java\nimport java.util.*;\n\nclass InventoryManager {\n private Map stock = new HashMap<>();\n\n public InventoryManager() {\n stock.put(\"LAPTOP\", 10);\n stock.put(\"PHONE\", 25);\n stock.put(\"TABLET\", 15);\n }\n\n public boolean checkStock(String productId, int quantity) {\n return stock.getOrDefault(productId, 0) >= quantity;\n }\n\n public void reduceStock(String productId, int quantity) {\n stock.put(productId, stock.get(productId) - quantity);\n }\n}\n\nclass NotificationService {\n public void sendOrderConfirmation(String customerEmail, String orderId, double total) {\n System.out.println(\"Email to \" + customerEmail + \": Order \" + orderId + \" confirmed. Total: $\" + total);\n }\n}\n\nclass OrderProcessor {\n private InventoryManager inventoryManager;\n private NotificationService notificationService;\n private int orderCounter = 0;\n\n public OrderProcessor(InventoryManager inventoryManager, NotificationService notificationService) {\n this.inventoryManager = inventoryManager;\n this.notificationService = notificationService;\n }\n\n public void placeOrder(String productId, int quantity, String customerEmail) {\n if (!inventoryManager.checkStock(productId, quantity)) {\n System.out.println(\"Insufficient stock for \" + productId);\n return;\n }\n inventoryManager.reduceStock(productId, quantity);\n double total = quantity * 100.0;\n orderCounter++;\n String orderId = \"ORD-\" + orderCounter;\n notificationService.sendOrderConfirmation(customerEmail, orderId, total);\n }\n}\n\npublic class Main {\n public static void main(String[] args) {\n InventoryManager inventory = new InventoryManager();\n NotificationService notifications = new NotificationService();\n OrderProcessor processor = new OrderProcessor(inventory, notifications);\n processor.placeOrder(\"LAPTOP\", 2, \"alice@example.com\");\n }\n}\n```\n\n```python\nclass InventoryManager:\n def __init__(self):\n self.stock = {\"LAPTOP\": 10, \"PHONE\": 25, \"TABLET\": 15}\n\n def check_stock(self, product_id, quantity):\n return self.stock.get(product_id, 0) >= quantity\n\n def reduce_stock(self, product_id, quantity):\n self.stock[product_id] -= quantity\n\nclass NotificationService:\n def send_order_confirmation(self, customer_email, order_id, total):\n print(f\"Email to {customer_email}: Order {order_id} confirmed. Total: ${total}\")\n\nclass OrderProcessor:\n def __init__(self, inventory_manager, notification_service):\n self.inventory_manager = inventory_manager\n self.notification_service = notification_service\n self.order_counter = 0\n\n def place_order(self, product_id, quantity, customer_email):\n if not self.inventory_manager.check_stock(product_id, quantity):\n print(f\"Insufficient stock for {product_id}\")\n return\n self.inventory_manager.reduce_stock(product_id, quantity)\n total = quantity * 100.0\n self.order_counter += 1\n order_id = f\"ORD-{self.order_counter}\"\n self.notification_service.send_order_confirmation(\n customer_email, order_id, total\n )\n\nif __name__ == \"__main__\":\n inventory = InventoryManager()\n notifications = NotificationService()\n processor = OrderProcessor(inventory, notifications)\n processor.place_order(\"LAPTOP\", 2, \"alice@example.com\")\n```\n\n```cpp\n#include \n#include \n#include \n#include \n\nusing namespace std;\n\nclass InventoryManager {\n unordered_map stock;\npublic:\n InventoryManager() {\n stock[\"LAPTOP\"] = 10;\n stock[\"PHONE\"] = 25;\n stock[\"TABLET\"] = 15;\n }\n\n bool checkStock(const string& productId, int quantity) {\n auto it = stock.find(productId);\n return it != stock.end() && it->second >= quantity;\n }\n\n void reduceStock(const string& productId, int quantity) {\n stock[productId] -= quantity;\n }\n};\n\nclass NotificationService {\npublic:\n void sendOrderConfirmation(const string& customerEmail,\n const string& orderId, double total) {\n cout << fixed << setprecision(1);\n cout << \"Email to \" << customerEmail << \": Order \" << orderId\n << \" confirmed. Total: $\" << total << endl;\n }\n};\n\nclass OrderProcessor {\n InventoryManager& inventoryManager;\n NotificationService& notificationService;\n int orderCounter = 0;\npublic:\n OrderProcessor(InventoryManager& inv, NotificationService& notif)\n : inventoryManager(inv), notificationService(notif) {}\n\n void placeOrder(const string& productId, int quantity,\n const string& customerEmail) {\n if (!inventoryManager.checkStock(productId, quantity)) {\n cout << \"Insufficient stock for \" << productId << endl;\n return;\n }\n inventoryManager.reduceStock(productId, quantity);\n double total = quantity * 100.0;\n orderCounter++;\n string orderId = \"ORD-\" + to_string(orderCounter);\n notificationService.sendOrderConfirmation(customerEmail, orderId, total);\n }\n};\n\nint main() {\n InventoryManager inventory;\n NotificationService notifications;\n OrderProcessor processor(inventory, notifications);\n processor.placeOrder(\"LAPTOP\", 2, \"alice@example.com\");\n return 0;\n}\n```\n\n```go\npackage main\n\nimport \"fmt\"\n\ntype InventoryManager struct {\n\tstock map[string]int\n}\n\nfunc NewInventoryManager() *InventoryManager {\n\treturn &InventoryManager{\n\t\tstock: map[string]int{\n\t\t\t\"LAPTOP\": 10,\n\t\t\t\"PHONE\": 25,\n\t\t\t\"TABLET\": 15,\n\t\t},\n\t}\n}\n\nfunc (im *InventoryManager) CheckStock(productID string, quantity int) bool {\n\treturn im.stock[productID] >= quantity\n}\n\nfunc (im *InventoryManager) ReduceStock(productID string, quantity int) {\n\tim.stock[productID] -= quantity\n}\n\ntype NotificationService struct{}\n\nfunc NewNotificationService() *NotificationService {\n\treturn &NotificationService{}\n}\n\nfunc (ns *NotificationService) SendOrderConfirmation(customerEmail, orderID string, total float64) {\n\tfmt.Printf(\"Email to %s: Order %s confirmed. Total: $%.1f\\n\", customerEmail, orderID, total)\n}\n\ntype OrderProcessor struct {\n\tinventoryManager *InventoryManager\n\tnotificationService *NotificationService\n\torderCounter int\n}\n\nfunc NewOrderProcessor(inventoryManager *InventoryManager, notificationService *NotificationService) *OrderProcessor {\n\treturn &OrderProcessor{\n\t\tinventoryManager: inventoryManager,\n\t\tnotificationService: notificationService,\n\t}\n}\n\nfunc (op *OrderProcessor) PlaceOrder(productID string, quantity int, customerEmail string) {\n\tif !op.inventoryManager.CheckStock(productID, quantity) {\n\t\tfmt.Printf(\"Insufficient stock for %s\\n\", productID)\n\t\treturn\n\t}\n\top.inventoryManager.ReduceStock(productID, quantity)\n\ttotal := float64(quantity) * 100.0\n\top.orderCounter++\n\torderID := fmt.Sprintf(\"ORD-%d\", op.orderCounter)\n\top.notificationService.SendOrderConfirmation(customerEmail, orderID, total)\n}\n\nfunc main() {\n\tinventory := NewInventoryManager()\n\tnotifications := NewNotificationService()\n\tprocessor := NewOrderProcessor(inventory, notifications)\n\tprocessor.PlaceOrder(\"LAPTOP\", 2, \"alice@example.com\")\n}\n```\n\n```csharp\nusing System;\nusing System.Collections.Generic;\n\nclass InventoryManager {\n private Dictionary stock = new Dictionary {\n { \"LAPTOP\", 10 }, { \"PHONE\", 25 }, { \"TABLET\", 15 }\n };\n\n public bool CheckStock(string productId, int quantity) {\n return stock.ContainsKey(productId) && stock[productId] >= quantity;\n }\n\n public void ReduceStock(string productId, int quantity) {\n stock[productId] -= quantity;\n }\n}\n\nclass NotificationService {\n public void SendOrderConfirmation(string customerEmail, string orderId, double total) {\n Console.WriteLine($\"Email to {customerEmail}: Order {orderId} confirmed. Total: ${total:F1}\");\n }\n}\n\nclass OrderProcessor {\n private InventoryManager inventoryManager;\n private NotificationService notificationService;\n private int orderCounter = 0;\n\n public OrderProcessor(InventoryManager inventoryManager, NotificationService notificationService) {\n this.inventoryManager = inventoryManager;\n this.notificationService = notificationService;\n }\n\n public void PlaceOrder(string productId, int quantity, string customerEmail) {\n if (!inventoryManager.CheckStock(productId, quantity)) {\n Console.WriteLine($\"Insufficient stock for {productId}\");\n return;\n }\n inventoryManager.ReduceStock(productId, quantity);\n double total = quantity * 100.0;\n orderCounter++;\n string orderId = \"ORD-\" + orderCounter;\n notificationService.SendOrderConfirmation(customerEmail, orderId, total);\n }\n}\n\nclass Program {\n static void Main() {\n var inventory = new InventoryManager();\n var notifications = new NotificationService();\n var processor = new OrderProcessor(inventory, notifications);\n processor.PlaceOrder(\"LAPTOP\", 2, \"alice@example.com\");\n }\n}\n```\n\n```typescript\nclass InventoryManager {\n private stock: Map;\n\n constructor() {\n this.stock = new Map([\n [\"LAPTOP\", 10],\n [\"PHONE\", 25],\n [\"TABLET\", 15],\n ]);\n }\n\n checkStock(productId: string, quantity: number): boolean {\n return (this.stock.get(productId) ?? 0) >= quantity;\n }\n\n reduceStock(productId: string, quantity: number): void {\n this.stock.set(productId, this.stock.get(productId)! - quantity);\n }\n}\n\nclass NotificationService {\n sendOrderConfirmation(customerEmail: string, orderId: string, total: number): void {\n console.log(`Email to ${customerEmail}: Order ${orderId} confirmed. Total: $${total.toFixed(1)}`);\n }\n}\n\nclass OrderProcessor {\n private inventoryManager: InventoryManager;\n private notificationService: NotificationService;\n private orderCounter = 0;\n\n constructor(inventoryManager: InventoryManager, notificationService: NotificationService) {\n this.inventoryManager = inventoryManager;\n this.notificationService = notificationService;\n }\n\n placeOrder(productId: string, quantity: number, customerEmail: string): void {\n if (!this.inventoryManager.checkStock(productId, quantity)) {\n console.log(`Insufficient stock for ${productId}`);\n return;\n }\n this.inventoryManager.reduceStock(productId, quantity);\n const total = quantity * 100.0;\n this.orderCounter++;\n const orderId = `ORD-${this.orderCounter}`;\n this.notificationService.sendOrderConfirmation(customerEmail, orderId, total);\n }\n}\n\nconst inventory = new InventoryManager();\nconst notifications = new NotificationService();\nconst processor = new OrderProcessor(inventory, notifications);\nprocessor.placeOrder(\"LAPTOP\", 2, \"alice@example.com\");\n```\n\n\n---\n\n# Exercise 2: ReportManager\n\n\n**Problem:** You have a `ReportManager` class that generates report data, formats it into a specific output (CSV, JSON), and distributes it via email. These are three distinct responsibilities bundled into one class. Your task is to refactor it into `ReportGenerator`, `ReportFormatter`, and `ReportDistributor`.\n\n**Requirements:**\n\n- `ReportGenerator` should gather and return raw report data (a list of records)\n- `ReportFormatter` should take raw data and format it as CSV text\n- `ReportDistributor` should take a formatted report and \"send\" it to a recipient\n- The main workflow should compose these three classes together\n\n```java\nimport java.util.*;\n\n// Before: One class doing three unrelated jobs\nclass ReportManager {\n public void createAndSendReport(String recipient) {\n // Responsibility 1: Generate report data\n List data = new ArrayList<>();\n data.add(new String[]{\"Name\", \"Sales\", \"Region\"});\n data.add(new String[]{\"Alice\", \"15000\", \"North\"});\n data.add(new String[]{\"Bob\", \"22000\", \"South\"});\n data.add(new String[]{\"Charlie\", \"18000\", \"East\"});\n\n // Responsibility 2: Format as CSV\n StringBuilder csv = new StringBuilder();\n for (String[] row : data) {\n csv.append(String.join(\",\", row)).append(\"\\n\");\n }\n\n // Responsibility 3: Distribute via email\n System.out.println(\"Sending report to: \" + recipient);\n System.out.println(csv.toString());\n System.out.println(\"Report sent successfully.\");\n }\n}\n\n// TODO: Refactor into ReportGenerator, ReportFormatter, and ReportDistributor.\n\npublic class Main {\n public static void main(String[] args) {\n // After refactoring, usage should look like:\n // ReportGenerator generator = new ReportGenerator();\n // ReportFormatter formatter = new ReportFormatter();\n // ReportDistributor distributor = new ReportDistributor();\n // List data = generator.generate();\n // String formatted = formatter.formatAsCsv(data);\n // distributor.distribute(\"manager@company.com\", formatted);\n }\n}\n```\n\n```python\n# Before: One class doing three unrelated jobs\nclass ReportManager:\n def create_and_send_report(self, recipient: str):\n # Responsibility 1: Generate report data\n data = [\n [\"Name\", \"Sales\", \"Region\"],\n [\"Alice\", \"15000\", \"North\"],\n [\"Bob\", \"22000\", \"South\"],\n [\"Charlie\", \"18000\", \"East\"],\n ]\n\n # Responsibility 2: Format as CSV\n csv_lines = []\n for row in data:\n csv_lines.append(\",\".join(row))\n csv_output = \"\\n\".join(csv_lines)\n\n # Responsibility 3: Distribute via email\n print(f\"Sending report to: {recipient}\")\n print(csv_output)\n print(\"Report sent successfully.\")\n\n# TODO: Refactor into ReportGenerator, ReportFormatter, and ReportDistributor.\n\nif __name__ == \"__main__\":\n # After refactoring, usage should look like:\n # generator = ReportGenerator()\n # formatter = ReportFormatter()\n # distributor = ReportDistributor()\n # data = generator.generate()\n # formatted = formatter.format_as_csv(data)\n # distributor.distribute(\"manager@company.com\", formatted)\n pass\n```\n\n```cpp\n#include \n#include \n#include \n#include \n\nusing namespace std;\n\n// Before: One class doing three unrelated jobs\nclass ReportManager {\npublic:\n void createAndSendReport(const string& recipient) {\n // Responsibility 1: Generate report data\n vector> data = {\n {\"Name\", \"Sales\", \"Region\"},\n {\"Alice\", \"15000\", \"North\"},\n {\"Bob\", \"22000\", \"South\"},\n {\"Charlie\", \"18000\", \"East\"}\n };\n\n // Responsibility 2: Format as CSV\n stringstream csv;\n for (const auto& row : data) {\n for (size_t i = 0; i < row.size(); i++) {\n if (i > 0) csv << \",\";\n csv << row[i];\n }\n csv << \"\\n\";\n }\n\n // Responsibility 3: Distribute via email\n cout << \"Sending report to: \" << recipient << endl;\n cout << csv.str();\n cout << \"Report sent successfully.\" << endl;\n }\n};\n\n// TODO: Refactor into ReportGenerator, ReportFormatter, and ReportDistributor.\n\nint main() {\n // After refactoring, usage should look like:\n // ReportGenerator generator;\n // ReportFormatter formatter;\n // ReportDistributor distributor;\n // auto data = generator.generate();\n // auto formatted = formatter.formatAsCsv(data);\n // distributor.distribute(\"manager@company.com\", formatted);\n return 0;\n}\n```\n\n```go\npackage main\n\nimport \"fmt\"\n\n// Before: One class doing three unrelated jobs\ntype ReportManager struct{}\n\nfunc (r *ReportManager) CreateAndSendReport(recipient string) {\n\t// Responsibility 1: Generate report data\n\tdata := [][]string{\n\t\t{\"Name\", \"Sales\", \"Region\"},\n\t\t{\"Alice\", \"15000\", \"North\"},\n\t\t{\"Bob\", \"22000\", \"South\"},\n\t\t{\"Charlie\", \"18000\", \"East\"},\n\t}\n\n\t// Responsibility 2: Format as CSV\n\tcsv := \"\"\n\tfor _, row := range data {\n\t\tfor i, value := range row {\n\t\t\tif i > 0 {\n\t\t\t\tcsv += \",\"\n\t\t\t}\n\t\t\tcsv += value\n\t\t}\n\t\tcsv += \"\\n\"\n\t}\n\n\t// Responsibility 3: Distribute via email\n\tfmt.Println(\"Sending report to:\", recipient)\n\tfmt.Print(csv)\n\tfmt.Println(\"Report sent successfully.\")\n}\n\n// TODO: Refactor into ReportGenerator, ReportFormatter, and ReportDistributor.\n\ntype ReportGenerator struct{}\n\nfunc (r *ReportGenerator) Generate() [][]string {\n\t// TODO: implement\n\treturn nil\n}\n\ntype ReportFormatter struct{}\n\nfunc (r *ReportFormatter) FormatAsCsv(data [][]string) string {\n\t// TODO: implement\n\treturn \"\"\n}\n\ntype ReportDistributor struct{}\n\nfunc (r *ReportDistributor) Distribute(recipient string, formatted string) {\n\t// TODO: implement\n}\n\nfunc main() {\n\t// After refactoring, usage should look like:\n\t// generator := ReportGenerator{}\n\t// formatter := ReportFormatter{}\n\t// distributor := ReportDistributor{}\n\t// data := generator.Generate()\n\t// formatted := formatter.FormatAsCsv(data)\n\t// distributor.Distribute(\"manager@company.com\", formatted)\n}\n```\n\n```csharp\nusing System;\nusing System.Collections.Generic;\nusing System.Text;\n\n// Before: One class doing three unrelated jobs\nclass ReportManager\n{\n public void CreateAndSendReport(string recipient)\n {\n // Responsibility 1: Generate report data\n var data = new List\n {\n new[] { \"Name\", \"Sales\", \"Region\" },\n new[] { \"Alice\", \"15000\", \"North\" },\n new[] { \"Bob\", \"22000\", \"South\" },\n new[] { \"Charlie\", \"18000\", \"East\" }\n };\n\n // Responsibility 2: Format as CSV\n var csv = new StringBuilder();\n foreach (var row in data)\n {\n csv.AppendLine(string.Join(\",\", row));\n }\n\n // Responsibility 3: Distribute via email\n Console.WriteLine(\"Sending report to: \" + recipient);\n Console.Write(csv.ToString());\n Console.WriteLine(\"Report sent successfully.\");\n }\n}\n\n// TODO: Refactor into ReportGenerator, ReportFormatter, and ReportDistributor.\n\nclass Program\n{\n static void Main()\n {\n // After refactoring, usage should look like:\n // var generator = new ReportGenerator();\n // var formatter = new ReportFormatter();\n // var distributor = new ReportDistributor();\n // var data = generator.Generate();\n // var formatted = formatter.FormatAsCsv(data);\n // distributor.Distribute(\"manager@company.com\", formatted);\n }\n}\n```\n\n```typescript\n// Before: One class doing three unrelated jobs\nclass ReportManager {\n createAndSendReport(recipient: string): void {\n // Responsibility 1: Generate report data\n const data: string[][] = [\n [\"Name\", \"Sales\", \"Region\"],\n [\"Alice\", \"15000\", \"North\"],\n [\"Bob\", \"22000\", \"South\"],\n [\"Charlie\", \"18000\", \"East\"],\n ];\n\n // Responsibility 2: Format as CSV\n const csv = data.map(row => row.join(\",\")).join(\"\\n\");\n\n // Responsibility 3: Distribute via email\n console.log(`Sending report to: ${recipient}`);\n console.log(csv);\n console.log(\"Report sent successfully.\");\n }\n}\n\n// TODO: Refactor into ReportGenerator, ReportFormatter, and ReportDistributor.\n\n// After refactoring, usage should look like:\n// const generator = new ReportGenerator();\n// const formatter = new ReportFormatter();\n// const distributor = new ReportDistributor();\n// const data = generator.generate();\n// const formatted = formatter.formatAsCsv(data);\n// distributor.distribute(\"manager@company.com\", formatted);\n```\n\n#### Solutions\n\n```java\nimport java.util.*;\n\nclass ReportGenerator {\n public List generate() {\n List data = new ArrayList<>();\n data.add(new String[]{\"Name\", \"Sales\", \"Region\"});\n data.add(new String[]{\"Alice\", \"15000\", \"North\"});\n data.add(new String[]{\"Bob\", \"22000\", \"South\"});\n data.add(new String[]{\"Charlie\", \"18000\", \"East\"});\n return data;\n }\n}\n\nclass ReportFormatter {\n public String formatAsCsv(List data) {\n StringBuilder sb = new StringBuilder();\n for (int i = 0; i < data.size(); i++) {\n sb.append(String.join(\",\", data.get(i)));\n if (i < data.size() - 1) {\n sb.append(\"\\n\");\n }\n }\n return sb.toString();\n }\n}\n\nclass ReportDistributor {\n public void distribute(String recipient, String formattedReport) {\n System.out.println(\"Sending report to: \" + recipient);\n System.out.println(formattedReport);\n System.out.println(\"Report sent successfully.\");\n }\n}\n\npublic class Main {\n public static void main(String[] args) {\n ReportGenerator generator = new ReportGenerator();\n ReportFormatter formatter = new ReportFormatter();\n ReportDistributor distributor = new ReportDistributor();\n\n List data = generator.generate();\n String csv = formatter.formatAsCsv(data);\n distributor.distribute(\"manager@company.com\", csv);\n }\n}\n```\n\n```python\nclass ReportGenerator:\n def generate(self):\n return [\n [\"Name\", \"Sales\", \"Region\"],\n [\"Alice\", \"15000\", \"North\"],\n [\"Bob\", \"22000\", \"South\"],\n [\"Charlie\", \"18000\", \"East\"],\n ]\n\nclass ReportFormatter:\n def format_as_csv(self, data):\n return \"\\n\".join(\",\".join(row) for row in data)\n\nclass ReportDistributor:\n def distribute(self, recipient, formatted_report):\n print(f\"Sending report to: {recipient}\")\n print(formatted_report)\n print(\"Report sent successfully.\")\n\nif __name__ == \"__main__\":\n generator = ReportGenerator()\n formatter = ReportFormatter()\n distributor = ReportDistributor()\n\n data = generator.generate()\n csv = formatter.format_as_csv(data)\n distributor.distribute(\"manager@company.com\", csv)\n```\n\n```cpp\n#include \n#include \n#include \n#include \n\nusing namespace std;\n\nclass ReportGenerator {\npublic:\n vector> generate() {\n return {\n {\"Name\", \"Sales\", \"Region\"},\n {\"Alice\", \"15000\", \"North\"},\n {\"Bob\", \"22000\", \"South\"},\n {\"Charlie\", \"18000\", \"East\"}\n };\n }\n};\n\nclass ReportFormatter {\npublic:\n string formatAsCsv(const vector>& data) {\n ostringstream oss;\n for (size_t i = 0; i < data.size(); i++) {\n for (size_t j = 0; j < data[i].size(); j++) {\n if (j > 0) oss << \",\";\n oss << data[i][j];\n }\n if (i < data.size() - 1) oss << \"\\n\";\n }\n return oss.str();\n }\n};\n\nclass ReportDistributor {\npublic:\n void distribute(const string& recipient, const string& formattedReport) {\n cout << \"Sending report to: \" << recipient << endl;\n cout << formattedReport << endl;\n cout << \"Report sent successfully.\" << endl;\n }\n};\n\nint main() {\n ReportGenerator generator;\n ReportFormatter formatter;\n ReportDistributor distributor;\n\n auto data = generator.generate();\n string csv = formatter.formatAsCsv(data);\n distributor.distribute(\"manager@company.com\", csv);\n return 0;\n}\n```\n\n```go\npackage main\n\nimport (\n\t\"fmt\"\n\t\"strings\"\n)\n\ntype ReportGenerator struct{}\n\nfunc (rg ReportGenerator) Generate() [][]string {\n\treturn [][]string{\n\t\t{\"Name\", \"Sales\", \"Region\"},\n\t\t{\"Alice\", \"15000\", \"North\"},\n\t\t{\"Bob\", \"22000\", \"South\"},\n\t\t{\"Charlie\", \"18000\", \"East\"},\n\t}\n}\n\ntype ReportFormatter struct{}\n\nfunc (rf ReportFormatter) FormatAsCsv(data [][]string) string {\n\tlines := make([]string, 0, len(data))\n\tfor _, row := range data {\n\t\tlines = append(lines, strings.Join(row, \",\"))\n\t}\n\treturn strings.Join(lines, \"\\n\")\n}\n\ntype ReportDistributor struct{}\n\nfunc (rd ReportDistributor) Distribute(recipient string, formattedReport string) {\n\tfmt.Println(\"Sending report to: \" + recipient)\n\tfmt.Println(formattedReport)\n\tfmt.Println(\"Report sent successfully.\")\n}\n\nfunc main() {\n\tgenerator := ReportGenerator{}\n\tformatter := ReportFormatter{}\n\tdistributor := ReportDistributor{}\n\n\tdata := generator.Generate()\n\tcsv := formatter.FormatAsCsv(data)\n\tdistributor.Distribute(\"manager@company.com\", csv)\n}\n```\n\n```csharp\nusing System;\nusing System.Collections.Generic;\n\nclass ReportGenerator {\n public List Generate() {\n return new List {\n new[] { \"Name\", \"Sales\", \"Region\" },\n new[] { \"Alice\", \"15000\", \"North\" },\n new[] { \"Bob\", \"22000\", \"South\" },\n new[] { \"Charlie\", \"18000\", \"East\" }\n };\n }\n}\n\nclass ReportFormatter {\n public string FormatAsCsv(List data) {\n var lines = new List();\n foreach (var row in data) {\n lines.Add(string.Join(\",\", row));\n }\n return string.Join(\"\\n\", lines);\n }\n}\n\nclass ReportDistributor {\n public void Distribute(string recipient, string formattedReport) {\n Console.WriteLine($\"Sending report to: {recipient}\");\n Console.WriteLine(formattedReport);\n Console.WriteLine(\"Report sent successfully.\");\n }\n}\n\nclass Program {\n static void Main() {\n var generator = new ReportGenerator();\n var formatter = new ReportFormatter();\n var distributor = new ReportDistributor();\n\n var data = generator.Generate();\n string csv = formatter.FormatAsCsv(data);\n distributor.Distribute(\"manager@company.com\", csv);\n }\n}\n```\n\n```typescript\nclass ReportGenerator {\n generate(): string[][] {\n return [\n [\"Name\", \"Sales\", \"Region\"],\n [\"Alice\", \"15000\", \"North\"],\n [\"Bob\", \"22000\", \"South\"],\n [\"Charlie\", \"18000\", \"East\"],\n ];\n }\n}\n\nclass ReportFormatter {\n formatAsCsv(data: string[][]): string {\n return data.map((row) => row.join(\",\")).join(\"\\n\");\n }\n}\n\nclass ReportDistributor {\n distribute(recipient: string, formattedReport: string): void {\n console.log(`Sending report to: ${recipient}`);\n console.log(formattedReport);\n console.log(\"Report sent successfully.\");\n }\n}\n\nconst generator = new ReportGenerator();\nconst formatter = new ReportFormatter();\nconst distributor = new ReportDistributor();\n\nconst data = generator.generate();\nconst csv = formatter.formatAsCsv(data);\ndistributor.distribute(\"manager@company.com\", csv);\n```\n","pageType":"lld-interviews"}

Exercise: Single Responsibility Principle

Exercise 1: OrderService God Class

Exercise 2: ReportManager

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