php - Parse error: syntax error, unexpected '(', expecting ',' or ';' in

I am recieveing the following parse error:

Parse error: syntax error, unexpected '(', expecting ',' or ';' in
H:\Programs\USBWebserver
v8.5\8.5\root\oopforum\func\register.class.php on line 7

which relates to the following line of code in my class:

private $random_name = rand(1000,9999).rand(1000,9999).rand(1000,9999).rand(1000,9999);

I can not see why this line of code would cause a parse error?

Here is some surrounding code:

class register{
    public $post_data = array();
        private $dbh;
        private $allowed_type = array('image/jpeg','image/png','image/gif');
        private $random_name = rand(1000,9999).rand(1000,9999).rand(1000,9999).rand(1000,9999);
        private $path = 'img/thumb_/'.$random_name. $_FILES['file']['name'];
        private $max_width = 4040;
        private $max_height = 4040;
        private $max_size = 5242880;
        private $temp_dir = $_FILES['file']['tmp_name'];
        private $image_type = $_FILES['file']['type'];
        private $image_size = $_FILES['file']['size'];
        private $image_name = $_FILES['file']['name'];
        private $image_dimensions = getimagesize($temp_dir);
        private $image_width = $image_dimensions[0]; // Image width
        private $image_height = $image_dimensions[1]; // Image height
        private $error = array();
        public function __construct($post_data, PDO $dbh){
        $this->post_data = array_map('trim', $post_data);
        $this->dbh = $dbh;
        }
}

What is causing the parse error?