<?php
class Account
{
    public string $owner;      // open to everyone
    protected string $bankId;  // this class and subclasses
    private float $balance = 0; // this class only

    public function __construct(string $owner)
    {
        $this->owner = $owner;
    }

    public function deposit(float $amount): void
    {
        $this->balance += $amount; // allowed: same class
    }

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

$acc = new Account("Sam");
$acc->deposit(100);
echo $acc->getBalance(); // 100
// echo $acc->balance;   // Error: balance is private
?>