Introduction to Encapsulation

// Anywhere in the codebase... UserAccount acc = new UserAccount(); acc.balance = -50000; // Negative balance? Sure, why not! acc.password = ""; // Empty password? No problem! acc.isActive = false; // Deactivate without proper procedure? Done!

// WITH encapsulation — controlled and safe class UserAccount { private String username; private String password; private double balance; private boolean isActive;

public UserAccount(String username, String password) { if (username.length() < 3) throw new IllegalArgumentException("Username too short"); if (password.length() < 8) throw new IllegalArgumentException("Password too weak"); this.username = username; this.password = hashPassword(password); this.balance = 0; this.isActive = true; }

public boolean deposit(double amount) { if (amount <= 0) return false; if (!isActive) return false; balance += amount; return true; }

public boolean withdraw(double amount) { if (amount <= 0) return false; if (amount > balance) return false; if (!isActive) return false; balance -= amount; return true; }

public double getBalance() { return balance; // Read-only access }

private String hashPassword(String raw) { // Internal implementation — hidden from outside return Integer.toHexString(raw.hashCode()); } }

class Thermostat: """Encapsulates temperature control logic"""

def __init__(self, target_temp=72): self.__current_temp = 68 # Private: sensor reading self.__target_temp = target_temp # Private: desired temp self.__is_heating = False # Private: system state self.__is_cooling = False

# Public interface — what users can do def set_target(self, temp): """Controlled access with validation""" if temp < 50 or temp > 90: raise ValueError("Temperature must be between 50°F and 90°F") self.__target_temp = temp self.__adjust()

def get_status(self): """Safe read access to state""" status = "idle" if self.__is_heating: status = "heating" if self.__is_cooling: status = "cooling" return { "current": self.__current_temp, "target": self.__target_temp, "status": status }

# Private implementation — hidden logic def __adjust(self): """Internal logic the user never sees""" diff = self.__target_temp - self.__current_temp self.__is_heating = diff > 2 self.__is_cooling = diff < -2

thermo = Thermostat(72) thermo.set_target(75) print(thermo.get_status())

Cannot do: thermo.__current_temp = 200 (AttributeError)

┌─────────────────────────────────────────┐ │ PUBLIC INTERFACE │ │ (what other code can see and use) │ │ │ │ deposit(), withdraw(), getBalance() │ ├─────────────────────────────────────────┤ │ PRIVATE IMPLEMENTATION │ │ (hidden internal details) │ │ │ │ balance, password, hashPassword(), │ │ validateTransaction(), auditLog │ └─────────────────────────────────────────┘