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HTML / CSS / JS

<?php
class BankAccount
{
    private float  $balance;    // no direct access from outside
    protected int  $ownerId;    // accessible in subclasses
    public string  $currency;   // fully public

public function __construct(int $ownerId, float $initialBalance = 0.0)
    {
        $this->ownerId  = $ownerId;
        $this->balance  = $initialBalance;
        $this->currency = 'USD';
    }

// Public interface — the only way to interact with balance
    public function deposit(float $amount): void
    {
        if ($amount <= 0) throw new \InvalidArgumentException('Amount must be positive');
        $this->balance += $amount;
        $this->logTransaction('deposit', $amount);
    }

public function withdraw(float $amount): void
    {
        if ($amount > $this->balance) throw new \RuntimeException('Insufficient funds');
        $this->balance -= $amount;
        $this->logTransaction('withdrawal', $amount);
    }

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

// Private — internal use only, not part of public API
    private function logTransaction(string $type, float $amount): void
    {
        echo sprintf("[LOG] %s: %.2f %s
", $type, $amount, $this->currency);
    }
}

$account = new BankAccount(1, 100.00);
$account->deposit(50.00);
$account->withdraw(30.00);
echo $account->getBalance(); // 120.00
// $account->balance; // Fatal error — private property