php程序模拟一个栈

<?phpclass stack{private $_data = array();private $_end = null;public function push($data){if($this->_end===null){$this->_end = 0;}else{$this->_end++;}$this->_data[$this->_end] = $data;}public function pop(){if(empty($this->_data))   return false;$ret = $this->_data[$this->_end];array_splice($this->_data,$this->_end);$this->_end--;}public function getData(){return $this->_data;}}$stack = new stack();$stack->push('d');$stack->push('e');$stack->push('f');$stack->pop();print_r($stack->getData());?>