Constructors and Visibility (public, private, protected)

Professional OOP code protects data using visibility.

Visibility explained

• public: accessible anywhere
• private: accessible only inside the class
• protected: accessible in class and child classes

Example: encapsulation

<?php
class BankAccount {
  private float $balance = 0;

  public function deposit(float $amount): void {
    if ($amount <= 0) return;
    $this->balance += $amount;
  }

  public function getBalance(): float {
    return $this->balance;
  }
}

$acc = new BankAccount();
$acc->deposit(100);
echo $acc->getBalance();
?>

Notice: balance cannot be changed directly, only through deposit.

Why this matters

Encapsulation prevents accidental bugs like negative balances.

Next: Inheritance, extending classes properly.