{"title":"Exercise: Interfaces","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: Log Formatter\n\n\n**Problem:** Build a logging system where the format of log messages is configurable. A `Logger` class writes log messages, but the format (plain text vs. JSON) is determined by an injected `Formatter` interface.\n\n**Requirements:**\n\n- `Formatter` interface with a `format(message)` method that takes a string and returns a formatted string\n- `PlainFormatter`: returns the message as-is (e.g., `\"Server started on port 8080\"`)\n- `JsonFormatter`: returns the message wrapped in JSON (e.g., `{\"log\": \"Server started on port 8080\"}`)\n- `Logger` class takes a `Formatter` in its constructor and has a `log(message)` method that formats the message, then prints it\n\n```java\ninterface Formatter {\n String format(String message);\n}\n\nclass PlainFormatter implements Formatter {\n public String format(String message) {\n // Return the message as-is\n return \"\";\n }\n}\n\nclass JsonFormatter implements Formatter {\n public String format(String message) {\n // Return the message wrapped in JSON: {\"log\": \"message\"}\n return \"\";\n }\n}\n\nclass Logger {\n private Formatter formatter;\n\n public Logger(Formatter formatter) {\n this.formatter = formatter;\n }\n\n public void log(String message) {\n // Use the formatter to format the message, then print the result\n }\n}\n\n// Test your implementation\npublic class Main {\n public static void main(String[] args) {\n Logger plainLogger = new Logger(new PlainFormatter());\n plainLogger.log(\"Server started on port 8080\");\n\n Logger jsonLogger = new Logger(new JsonFormatter());\n jsonLogger.log(\"Server started on port 8080\");\n }\n}\n```\n\n```python\nfrom abc import ABC, abstractmethod\n\nclass Formatter(ABC):\n @abstractmethod\n def format(self, message: str) -> str:\n pass\n\nclass PlainFormatter(Formatter):\n def format(self, message: str) -> str:\n # Return the message as-is\n return \"\"\n\nclass JsonFormatter(Formatter):\n def format(self, message: str) -> str:\n # Return the message wrapped in JSON: {\"log\": \"message\"}\n return \"\"\n\nclass Logger:\n def __init__(self, formatter: Formatter):\n self._formatter = formatter\n\n def log(self, message: str) -> None:\n # Use the formatter to format the message, then print the result\n pass\n\nif __name__ == \"__main__\":\n plain_logger = Logger(PlainFormatter())\n plain_logger.log(\"Server started on port 8080\")\n\n json_logger = Logger(JsonFormatter())\n json_logger.log(\"Server started on port 8080\")\n```\n\n```cpp\n#include \n#include \nusing namespace std;\n\nclass Formatter {\npublic:\n virtual ~Formatter() {}\n virtual string format(const string& message) = 0;\n};\n\nclass PlainFormatter : public Formatter {\npublic:\n string format(const string& message) override {\n // Return the message as-is\n return \"\";\n }\n};\n\nclass JsonFormatter : public Formatter {\npublic:\n string format(const string& message) override {\n // Return the message wrapped in JSON: {\"log\": \"message\"}\n return \"\";\n }\n};\n\nclass Logger {\n Formatter* formatter;\npublic:\n Logger(Formatter* formatter) : formatter(formatter) {}\n\n void log(const string& message) {\n // Use the formatter to format the message, then print the result\n }\n};\n\nint main() {\n PlainFormatter plain;\n Logger plainLogger(&plain);\n plainLogger.log(\"Server started on port 8080\");\n\n JsonFormatter json;\n Logger jsonLogger(&json);\n jsonLogger.log(\"Server started on port 8080\");\n\n return 0;\n}\n```\n\n```go\npackage main\n\nimport \"fmt\"\n\ntype Formatter interface {\n\tFormat(message string) string\n}\n\ntype PlainFormatter struct{}\n\nfunc (p *PlainFormatter) Format(message string) string {\n\t// Return the message as-is\n\treturn \"\"\n}\n\ntype JsonFormatter struct{}\n\nfunc (j *JsonFormatter) Format(message string) string {\n\t// Return the message wrapped in JSON: {\"log\": \"message\"}\n\treturn \"\"\n}\n\ntype Logger struct {\n\tformatter Formatter\n}\n\nfunc NewLogger(formatter Formatter) *Logger {\n\treturn &Logger{\n\t\tformatter: formatter,\n\t}\n}\n\nfunc (l *Logger) Log(message string) {\n\t// Use the formatter to format the message, then print the result\n\t_ = message\n\tfmt.Println(\"\")\n}\n\nfunc main() {\n\tplainLogger := NewLogger(&PlainFormatter{})\n\tplainLogger.Log(\"Server started on port 8080\")\n\n\tjsonLogger := NewLogger(&JsonFormatter{})\n\tjsonLogger.Log(\"Server started on port 8080\")\n}\n```\n\n```csharp\nusing System;\n\npublic interface IFormatter\n{\n string Format(string message);\n}\n\npublic class PlainFormatter : IFormatter\n{\n public string Format(string message)\n {\n // Return the message as-is\n return \"\";\n }\n}\n\npublic class JsonFormatter : IFormatter\n{\n public string Format(string message)\n {\n // Return the message wrapped in JSON: {\"log\": \"message\"}\n return \"\";\n }\n}\n\npublic class Logger\n{\n private IFormatter _formatter;\n\n public Logger(IFormatter formatter)\n {\n _formatter = formatter;\n }\n\n public void Log(string message)\n {\n // Use the formatter to format the message, then print the result\n }\n}\n\npublic class Program\n{\n public static void Main()\n {\n var plainLogger = new Logger(new PlainFormatter());\n plainLogger.Log(\"Server started on port 8080\");\n\n var jsonLogger = new Logger(new JsonFormatter());\n jsonLogger.Log(\"Server started on port 8080\");\n }\n}\n```\n\n```typescript\ninterface Formatter {\n format(message: string): string;\n}\n\nclass PlainFormatter implements Formatter {\n format(message: string): string {\n // Return the message as-is\n return \"\";\n }\n}\n\nclass JsonFormatter implements Formatter {\n format(message: string): string {\n // Return the message wrapped in JSON: {\"log\": \"message\"}\n return \"\";\n }\n}\n\nclass Logger {\n private formatter: Formatter;\n\n constructor(formatter: Formatter) {\n this.formatter = formatter;\n }\n\n log(message: string): void {\n // Use the formatter to format the message, then print the result\n }\n}\n\n// Test your implementation\nconst plainLogger = new Logger(new PlainFormatter());\nplainLogger.log(\"Server started on port 8080\");\n\nconst jsonLogger = new Logger(new JsonFormatter());\njsonLogger.log(\"Server started on port 8080\");\n```\n\n#### Solutions\n\n```java\ninterface Formatter {\n String format(String message);\n}\n\nclass PlainFormatter implements Formatter {\n public String format(String message) {\n return message;\n }\n}\n\nclass JsonFormatter implements Formatter {\n public String format(String message) {\n return \"{\\\"log\\\": \\\"\" + message + \"\\\"}\";\n }\n}\n\nclass Logger {\n private Formatter formatter;\n\n public Logger(Formatter formatter) {\n this.formatter = formatter;\n }\n\n public void log(String message) {\n System.out.println(formatter.format(message));\n }\n}\n\npublic class Main {\n public static void main(String[] args) {\n Logger plainLogger = new Logger(new PlainFormatter());\n plainLogger.log(\"Server started on port 8080\");\n\n Logger jsonLogger = new Logger(new JsonFormatter());\n jsonLogger.log(\"Server started on port 8080\");\n }\n}\n```\n\n```python\nfrom abc import ABC, abstractmethod\n\nclass Formatter(ABC):\n @abstractmethod\n def format(self, message: str) -> str:\n pass\n\nclass PlainFormatter(Formatter):\n def format(self, message: str) -> str:\n return message\n\nclass JsonFormatter(Formatter):\n def format(self, message: str) -> str:\n return '{\"log\": \"' + message + '\"}'\n\nclass Logger:\n def __init__(self, formatter: Formatter):\n self._formatter = formatter\n\n def log(self, message: str) -> None:\n print(self._formatter.format(message))\n\nif __name__ == \"__main__\":\n plain_logger = Logger(PlainFormatter())\n plain_logger.log(\"Server started on port 8080\")\n\n json_logger = Logger(JsonFormatter())\n json_logger.log(\"Server started on port 8080\")\n```\n\n```cpp\n#include \n#include \nusing namespace std;\n\nclass Formatter {\npublic:\n virtual ~Formatter() {}\n virtual string format(const string& message) = 0;\n};\n\nclass PlainFormatter : public Formatter {\npublic:\n string format(const string& message) override {\n return message;\n }\n};\n\nclass JsonFormatter : public Formatter {\npublic:\n string format(const string& message) override {\n return \"{\\\"log\\\": \\\"\" + message + \"\\\"}\";\n }\n};\n\nclass Logger {\n Formatter* formatter;\npublic:\n Logger(Formatter* formatter) : formatter(formatter) {}\n\n void log(const string& message) {\n cout << formatter->format(message) << endl;\n }\n};\n\nint main() {\n PlainFormatter plain;\n Logger plainLogger(&plain);\n plainLogger.log(\"Server started on port 8080\");\n\n JsonFormatter json;\n Logger jsonLogger(&json);\n jsonLogger.log(\"Server started on port 8080\");\n\n return 0;\n}\n```\n\n```go\npackage main\n\nimport \"fmt\"\n\ntype Formatter interface {\n\tFormat(message string) string\n}\n\ntype PlainFormatter struct{}\n\nfunc (p PlainFormatter) Format(message string) string {\n\treturn message\n}\n\ntype JsonFormatter struct{}\n\nfunc (j JsonFormatter) Format(message string) string {\n\treturn \"{\\\"log\\\": \\\"\" + message + \"\\\"}\"\n}\n\ntype Logger struct {\n\tformatter Formatter\n}\n\nfunc NewLogger(formatter Formatter) *Logger {\n\treturn &Logger{formatter: formatter}\n}\n\nfunc (l *Logger) Log(message string) {\n\tfmt.Println(l.formatter.Format(message))\n}\n\nfunc main() {\n\tplainLogger := NewLogger(PlainFormatter{})\n\tplainLogger.Log(\"Server started on port 8080\")\n\n\tjsonLogger := NewLogger(JsonFormatter{})\n\tjsonLogger.Log(\"Server started on port 8080\")\n}\n```\n\n```csharp\nusing System;\n\npublic interface IFormatter\n{\n string Format(string message);\n}\n\npublic class PlainFormatter : IFormatter\n{\n public string Format(string message)\n {\n return message;\n }\n}\n\npublic class JsonFormatter : IFormatter\n{\n public string Format(string message)\n {\n return \"{\\\"log\\\": \\\"\" + message + \"\\\"}\";\n }\n}\n\npublic class Logger\n{\n private IFormatter _formatter;\n\n public Logger(IFormatter formatter)\n {\n _formatter = formatter;\n }\n\n public void Log(string message)\n {\n Console.WriteLine(_formatter.Format(message));\n }\n}\n\npublic class Program\n{\n public static void Main()\n {\n var plainLogger = new Logger(new PlainFormatter());\n plainLogger.Log(\"Server started on port 8080\");\n\n var jsonLogger = new Logger(new JsonFormatter());\n jsonLogger.Log(\"Server started on port 8080\");\n }\n}\n```\n\n```typescript\ninterface Formatter {\n format(message: string): string;\n}\n\nclass PlainFormatter implements Formatter {\n format(message: string): string {\n return message;\n }\n}\n\nclass JsonFormatter implements Formatter {\n format(message: string): string {\n return `{\"log\": \"${message}\"}`;\n }\n}\n\nclass Logger {\n private formatter: Formatter;\n\n constructor(formatter: Formatter) {\n this.formatter = formatter;\n }\n\n log(message: string): void {\n console.log(this.formatter.format(message));\n }\n}\n\nconst plainLogger = new Logger(new PlainFormatter());\nplainLogger.log(\"Server started on port 8080\");\n\nconst jsonLogger = new Logger(new JsonFormatter());\njsonLogger.log(\"Server started on port 8080\");\n```\n\n\n---\n\n# Exercise 2: Input Validator\n\n\n**Problem:** Build a registration system where multiple validation rules are applied to user input. Each rule is a separate implementation of a `Validator` interface, and the `RegistrationService` runs all validators before accepting the registration.\n\n**Requirements:**\n\n- `Validator` interface with a `validate(input)` method that returns `true` if valid, `false` otherwise\n- `EmailValidator`: returns `true` if the input contains `@`\n- `PasswordValidator`: returns `true` if the input has 8 or more characters\n- `RegistrationService`: takes a list of validators in its constructor. Its `register(input)` method runs all validators and prints whether the input passed or failed\n\n```java\nimport java.util.List;\n\ninterface Validator {\n boolean validate(String input);\n}\n\nclass EmailValidator implements Validator {\n public boolean validate(String input) {\n // Return true if input contains \"@\"\n return false;\n }\n}\n\nclass PasswordValidator implements Validator {\n public boolean validate(String input) {\n // Return true if input.length() >= 8\n return false;\n }\n}\n\nclass RegistrationService {\n private List validators;\n\n public RegistrationService(List validators) {\n this.validators = validators;\n }\n\n public void register(String input) {\n // Run all validators on input. If all pass, print \"input\" - PASSED\n // If any fail, print \"input\" - FAILED\n }\n}\n\n// Test your implementation\npublic class Main {\n public static void main(String[] args) {\n List emailValidators = List.of(new EmailValidator());\n RegistrationService emailReg = new RegistrationService(emailValidators);\n emailReg.register(\"user@example.com\"); // Should pass\n emailReg.register(\"invalid-email\"); // Should fail\n\n List passwordValidators = List.of(new PasswordValidator());\n RegistrationService passReg = new RegistrationService(passwordValidators);\n passReg.register(\"strongpassword\"); // Should pass\n passReg.register(\"short\"); // Should fail\n }\n}\n```\n\n```python\nfrom abc import ABC, abstractmethod\n\nclass Validator(ABC):\n @abstractmethod\n def validate(self, input: str) -> bool:\n pass\n\nclass EmailValidator(Validator):\n def validate(self, input: str) -> bool:\n # Return True if \"@\" in input\n return False\n\nclass PasswordValidator(Validator):\n def validate(self, input: str) -> bool:\n # Return True if len(input) >= 8\n return False\n\nclass RegistrationService:\n def __init__(self, validators: list[Validator]):\n self._validators = validators\n\n def register(self, input: str) -> None:\n # Run all validators on input. If all pass, print \"input\" - PASSED\n # If any fail, print \"input\" - FAILED\n pass\n\nif __name__ == \"__main__\":\n email_reg = RegistrationService([EmailValidator()])\n email_reg.register(\"user@example.com\") # Should pass\n email_reg.register(\"invalid-email\") # Should fail\n\n pass_reg = RegistrationService([PasswordValidator()])\n pass_reg.register(\"strongpassword\") # Should pass\n pass_reg.register(\"short\") # Should fail\n```\n\n```cpp\n#include \n#include \n#include \nusing namespace std;\n\nclass Validator {\npublic:\n virtual ~Validator() {}\n virtual bool validate(const string& input) = 0;\n};\n\nclass EmailValidator : public Validator {\npublic:\n bool validate(const string& input) override {\n // Return true if input contains \"@\"\n return false;\n }\n};\n\nclass PasswordValidator : public Validator {\npublic:\n bool validate(const string& input) override {\n // Return true if input.length() >= 8\n return false;\n }\n};\n\nclass RegistrationService {\n vector validators;\npublic:\n RegistrationService(const vector& validators)\n : validators(validators) {}\n\n void registerInput(const string& input) {\n // Run all validators on input. If all pass, print \"input\" - PASSED\n // If any fail, print \"input\" - FAILED\n }\n};\n\nint main() {\n EmailValidator emailVal;\n vector emailValidators = {&emailVal};\n RegistrationService emailReg(emailValidators);\n emailReg.registerInput(\"user@example.com\"); // Should pass\n emailReg.registerInput(\"invalid-email\"); // Should fail\n\n PasswordValidator passVal;\n vector passValidators = {&passVal};\n RegistrationService passReg(passValidators);\n passReg.registerInput(\"strongpassword\"); // Should pass\n passReg.registerInput(\"short\"); // Should fail\n\n return 0;\n}\n```\n\n```go\npackage main\n\ntype Validator interface {\n\tValidate(input string) bool\n}\n\ntype EmailValidator struct{}\n\nfunc (e *EmailValidator) Validate(input string) bool {\n\t// Return true if input contains \"@\"\n\treturn false\n}\n\ntype PasswordValidator struct{}\n\nfunc (p *PasswordValidator) Validate(input string) bool {\n\t// Return true if input.length() >= 8\n\treturn false\n}\n\ntype RegistrationService struct {\n\tvalidators []Validator\n}\n\nfunc NewRegistrationService(validators []Validator) *RegistrationService {\n\treturn &RegistrationService{\n\t\tvalidators: validators,\n\t}\n}\n\nfunc (r *RegistrationService) Register(input string) {\n\t// Run all validators on input. If all pass, print \"input\" - PASSED\n\t// If any fail, print \"input\" - FAILED\n}\n\nfunc main() {\n\temailReg := NewRegistrationService([]Validator{&EmailValidator{}})\n\temailReg.Register(\"user@example.com\") // Should pass\n\temailReg.Register(\"invalid-email\") // Should fail\n\n\tpassReg := NewRegistrationService([]Validator{&PasswordValidator{}})\n\tpassReg.Register(\"strongpassword\") // Should pass\n\tpassReg.Register(\"short\") // Should fail\n}\n```\n\n```csharp\nusing System;\nusing System.Collections.Generic;\n\npublic interface IValidator\n{\n bool Validate(string input);\n}\n\npublic class EmailValidator : IValidator\n{\n public bool Validate(string input)\n {\n // Return true if input contains \"@\"\n return false;\n }\n}\n\npublic class PasswordValidator : IValidator\n{\n public bool Validate(string input)\n {\n // Return true if input.Length >= 8\n return false;\n }\n}\n\npublic class RegistrationService\n{\n private List _validators;\n\n public RegistrationService(List validators)\n {\n _validators = validators;\n }\n\n public void Register(string input)\n {\n // Run all validators on input. If all pass, print \"input\" - PASSED\n // If any fail, print \"input\" - FAILED\n }\n}\n\npublic class Program\n{\n public static void Main()\n {\n var emailReg = new RegistrationService(new List { new EmailValidator() });\n emailReg.Register(\"user@example.com\"); // Should pass\n emailReg.Register(\"invalid-email\"); // Should fail\n\n var passReg = new RegistrationService(new List { new PasswordValidator() });\n passReg.Register(\"strongpassword\"); // Should pass\n passReg.Register(\"short\"); // Should fail\n }\n}\n```\n\n```typescript\ninterface Validator {\n validate(input: string): boolean;\n}\n\nclass EmailValidator implements Validator {\n validate(input: string): boolean {\n // Return true if input includes \"@\"\n return false;\n }\n}\n\nclass PasswordValidator implements Validator {\n validate(input: string): boolean {\n // Return true if input.length >= 8\n return false;\n }\n}\n\nclass RegistrationService {\n private validators: Validator[];\n\n constructor(validators: Validator[]) {\n this.validators = validators;\n }\n\n register(input: string): void {\n // Run all validators on input. If all pass, print \"input\" - PASSED\n // If any fail, print \"input\" - FAILED\n }\n}\n\n// Test your implementation\nconst emailReg = new RegistrationService([new EmailValidator()]);\nemailReg.register(\"user@example.com\"); // Should pass\nemailReg.register(\"invalid-email\"); // Should fail\n\nconst passReg = new RegistrationService([new PasswordValidator()]);\npassReg.register(\"strongpassword\"); // Should pass\npassReg.register(\"short\"); // Should fail\n```\n\n#### Solutions\n\n```java\nimport java.util.List;\n\ninterface Validator {\n boolean validate(String input);\n}\n\nclass EmailValidator implements Validator {\n public boolean validate(String input) {\n return input.contains(\"@\");\n }\n}\n\nclass PasswordValidator implements Validator {\n public boolean validate(String input) {\n return input.length() >= 8;\n }\n}\n\nclass RegistrationService {\n private List validators;\n\n public RegistrationService(List validators) {\n this.validators = validators;\n }\n\n public void register(String input) {\n boolean allPassed = true;\n for (Validator validator : validators) {\n if (!validator.validate(input)) {\n allPassed = false;\n break;\n }\n }\n System.out.println(\"\\\"\" + input + \"\\\" - \" + (allPassed ? \"PASSED\" : \"FAILED\"));\n }\n}\n\npublic class Main {\n public static void main(String[] args) {\n List emailValidators = List.of(new EmailValidator());\n RegistrationService emailReg = new RegistrationService(emailValidators);\n emailReg.register(\"user@example.com\");\n emailReg.register(\"invalid-email\");\n\n List passwordValidators = List.of(new PasswordValidator());\n RegistrationService passReg = new RegistrationService(passwordValidators);\n passReg.register(\"strongpassword\");\n passReg.register(\"short\");\n }\n}\n```\n\n```python\nfrom abc import ABC, abstractmethod\n\nclass Validator(ABC):\n @abstractmethod\n def validate(self, input: str) -> bool:\n pass\n\nclass EmailValidator(Validator):\n def validate(self, input: str) -> bool:\n return \"@\" in input\n\nclass PasswordValidator(Validator):\n def validate(self, input: str) -> bool:\n return len(input) >= 8\n\nclass RegistrationService:\n def __init__(self, validators: list[Validator]):\n self._validators = validators\n\n def register(self, input: str) -> None:\n all_passed = all(v.validate(input) for v in self._validators)\n result = \"PASSED\" if all_passed else \"FAILED\"\n print(f'\"{input}\" - {result}')\n\nif __name__ == \"__main__\":\n email_reg = RegistrationService([EmailValidator()])\n email_reg.register(\"user@example.com\")\n email_reg.register(\"invalid-email\")\n\n pass_reg = RegistrationService([PasswordValidator()])\n pass_reg.register(\"strongpassword\")\n pass_reg.register(\"short\")\n```\n\n```cpp\n#include \n#include \n#include \nusing namespace std;\n\nclass Validator {\npublic:\n virtual ~Validator() {}\n virtual bool validate(const string& input) = 0;\n};\n\nclass EmailValidator : public Validator {\npublic:\n bool validate(const string& input) override {\n return input.find('@') != string::npos;\n }\n};\n\nclass PasswordValidator : public Validator {\npublic:\n bool validate(const string& input) override {\n return input.length() >= 8;\n }\n};\n\nclass RegistrationService {\n vector validators;\npublic:\n RegistrationService(const vector& validators)\n : validators(validators) {}\n\n void registerInput(const string& input) {\n bool allPassed = true;\n for (auto* validator : validators) {\n if (!validator->validate(input)) {\n allPassed = false;\n break;\n }\n }\n cout << \"\\\"\" << input << \"\\\" - \" << (allPassed ? \"PASSED\" : \"FAILED\") << endl;\n }\n};\n\nint main() {\n EmailValidator emailVal;\n vector emailValidators = {&emailVal};\n RegistrationService emailReg(emailValidators);\n emailReg.registerInput(\"user@example.com\");\n emailReg.registerInput(\"invalid-email\");\n\n PasswordValidator passVal;\n vector passValidators = {&passVal};\n RegistrationService passReg(passValidators);\n passReg.registerInput(\"strongpassword\");\n passReg.registerInput(\"short\");\n\n return 0;\n}\n```\n\n```go\npackage main\n\nimport (\n\t\"fmt\"\n\t\"strings\"\n)\n\ntype Validator interface {\n\tValidate(input string) bool\n}\n\ntype EmailValidator struct{}\n\nfunc (e EmailValidator) Validate(input string) bool {\n\treturn strings.Contains(input, \"@\")\n}\n\ntype PasswordValidator struct{}\n\nfunc (p PasswordValidator) Validate(input string) bool {\n\treturn len(input) >= 8\n}\n\ntype RegistrationService struct {\n\tvalidators []Validator\n}\n\nfunc NewRegistrationService(validators []Validator) *RegistrationService {\n\treturn &RegistrationService{validators: validators}\n}\n\nfunc (r *RegistrationService) Register(input string) {\n\tallPassed := true\n\tfor _, validator := range r.validators {\n\t\tif !validator.Validate(input) {\n\t\t\tallPassed = false\n\t\t\tbreak\n\t\t}\n\t}\n\tresult := \"FAILED\"\n\tif allPassed {\n\t\tresult = \"PASSED\"\n\t}\n\tfmt.Printf(\"\\\"%s\\\" - %s\\n\", input, result)\n}\n\nfunc main() {\n\temailReg := NewRegistrationService([]Validator{EmailValidator{}})\n\temailReg.Register(\"user@example.com\")\n\temailReg.Register(\"invalid-email\")\n\n\tpassReg := NewRegistrationService([]Validator{PasswordValidator{}})\n\tpassReg.Register(\"strongpassword\")\n\tpassReg.Register(\"short\")\n}\n```\n\n```csharp\nusing System;\nusing System.Collections.Generic;\nusing System.Linq;\n\npublic interface IValidator\n{\n bool Validate(string input);\n}\n\npublic class EmailValidator : IValidator\n{\n public bool Validate(string input)\n {\n return input.Contains(\"@\");\n }\n}\n\npublic class PasswordValidator : IValidator\n{\n public bool Validate(string input)\n {\n return input.Length >= 8;\n }\n}\n\npublic class RegistrationService\n{\n private List _validators;\n\n public RegistrationService(List validators)\n {\n _validators = validators;\n }\n\n public void Register(string input)\n {\n bool allPassed = _validators.All(v => v.Validate(input));\n Console.WriteLine($\"\\\"{input}\\\" - {(allPassed ? \"PASSED\" : \"FAILED\")}\");\n }\n}\n\npublic class Program\n{\n public static void Main()\n {\n var emailReg = new RegistrationService(new List { new EmailValidator() });\n emailReg.Register(\"user@example.com\");\n emailReg.Register(\"invalid-email\");\n\n var passReg = new RegistrationService(new List { new PasswordValidator() });\n passReg.Register(\"strongpassword\");\n passReg.Register(\"short\");\n }\n}\n```\n\n```typescript\ninterface Validator {\n validate(input: string): boolean;\n}\n\nclass EmailValidator implements Validator {\n validate(input: string): boolean {\n return input.includes(\"@\");\n }\n}\n\nclass PasswordValidator implements Validator {\n validate(input: string): boolean {\n return input.length >= 8;\n }\n}\n\nclass RegistrationService {\n private validators: Validator[];\n\n constructor(validators: Validator[]) {\n this.validators = validators;\n }\n\n register(input: string): void {\n const allPassed = this.validators.every(v => v.validate(input));\n console.log(`\"${input}\" - ${allPassed ? \"PASSED\" : \"FAILED\"}`);\n }\n}\n\nconst emailReg = new RegistrationService([new EmailValidator()]);\nemailReg.register(\"user@example.com\");\nemailReg.register(\"invalid-email\");\n\nconst passReg = new RegistrationService([new PasswordValidator()]);\npassReg.register(\"strongpassword\");\npassReg.register(\"short\");\n```\n","pageType":"lld-interviews"}

Exercise 1: Log Formatter

Exercise 2: Input Validator

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