Single Responsibility Principle

// ❌ SRP Violation
// BAD: User class does authentication, database, AND email
public class User {
    public void authenticate(String user, String pass) { /* ... */ }
    public void saveToDatabase() { /* ... */ }
    public void sendEmail(String msg) { /* ... */ }
    public void generateReport() { /* ... */ }
}

// ✅ SRP Applied
// GOOD: Each class has a single responsibility
public class User {
    private String name;
    private String email;
    // Only user data and behavior
}

public class AuthenticationService {
    public boolean authenticate(String username, String password) {
        // Only handles authentication
        return true;
    }
}

public class UserRepository {
    public void save(User user) {
        // Only handles persistence
    }
    public User findById(String id) { return null; }
}

public class EmailService {
    public void sendEmail(String to, String subject, String body) {
        // Only handles email sending
    }
}

public class ReportGenerator {
    public String generateReport(User user) {
        // Only handles report generation
        return "";
    }
}