PHP Access Modifiers

Access Modifiers (public, protected, private) & Encapsulation

Access modifiers control the visibility and scope accessibility of class properties and methods from outside the class or from inherited child classes.

Access Modifier Visibility Matrix

Visibility Scope Architecture

flowchart TD
    A["Class Instance Object"] --> B["public: Accessible from anywhere"]
    A --> C["protected: Accessible in class & derived child subclasses"]
    A --> D["private: Enclosed strictly inside defining class scope"]

Practical Code Example

<?php
declare(strict_types=1);

class BankAccount
{
    public string $accountHolder;    // Public: Accessible anywhere
    protected string $accountType;   // Protected: Accessible in child classes
    private float $balance;          // Private: Accessible ONLY in BankAccount

    public function __construct(string $holder, string $type, float $initialDeposit)
    {
        $this->accountHolder = $holder;
        $this->accountType = $type;
        $this->balance = max(0.0, $initialDeposit);
    }

    // Encapsulated getter for private property
    public function getBalance(): float
    {
        return $this->balance;
    }

    // Encapsulated method with validation controls
    public function deposit(float $amount): void
    {
        if ($amount > 0) {
            $this->balance += $amount;
        }
    }
}

class SavingsAccount extends BankAccount
{
    public function getAccountDetails(): string
    {
        // Can access $this->accountType (protected), but NOT $this->balance (private)!
        return "Holder: {$this->accountHolder} | Type: {$this->accountType} | Balance: $" . $this->getBalance();
    }
}

$account = new SavingsAccount("Maksudur", "High-Yield Savings", 1500.00);
echo $account->getAccountDetails() . "
";

// Attempting to access $account->balance directly throws a Fatal Uncaught Error!

Best Practices

• Default to private or protected Properties: Protect internal state from direct external modification.
• Expose Intentional Public Methods: Provide explicit public getter and setter methods that validate state changes.
• Use protected for Extendable Base Classes: Use protected if you anticipate child subclasses extending and referencing internal properties.

Self-Check Challenge

Which access modifier allows property access inside the defining class and its subclasses, but forbids external access? (protected)