1<?php
2class BankAccount
3{
4    protected $balance = 0;
5
6    public function getBalance()
7    {
8        return $this->balance;
9    }
10
11    protected function setBalance($balance)
12    {
13        if ($balance >= 0) {
14            $this->balance = $balance;
15        } else {
16            throw new RuntimeException;
17        }
18    }
19
20    public function depositMoney($balance)
21    {
22        $this->setBalance($this->getBalance() + $balance);
23
24        return $this->getBalance();
25    }
26
27    public function withdrawMoney($balance)
28    {
29        $this->setBalance($this->getBalance() - $balance);
30
31        return $this->getBalance();
32    }
33}
34