Login username and password validator written in PHP

/**
 * Validator for Login.
*/
final class LoginValidator {
 private function __construct() {

 }
 /**
     * Validate the given username and password.
     * @param $username and $password to be validated
     * @return array array of {@link Error} s
*/
 public static function validate($username, $password) {
 $errors = array();
 $username = trim($username);
 if (! $username) {
 $errors[] = new Error('username', 'Username cannot be empty.');
 } elseif (strlen($username)<3) {
 $errors[] = new Error( 'username', 'The username cannot be less than 3 characters long');
 } elseif (strlen($username)>30) {
 $errors[] = new Error('username', 'The username cannot be longer than 3 characters. 30 characters. ');
 } elseif (!preg_match('/^[A-Za-z]+$/',substr($username, 0, 1))) {
 $errors[] = new Error( 'username', 'Username must start with a letter. ');
 } elseif (!preg_match('/^[A-Za-z0-9_]+$/', $username)) {
 $errors[] = new Error('username', 'Username can only be a combination of letters, numbers and underscores (_).');
 } elseif (!trim($password)) {
 $errors[] = new Error('password ', 'Password cannot be empty. ');
 } else {
 // check whether use exists or not
 $dao = new UserDao();
 $user = $dao->findByName($username);< /p>
 if ($user) {
 if (!($user->getPassword() == sha1($user->getSalt() . $password))) {
 $errors[ ] = new Error('password', 'Wrong username or password. ');
 }
 } else {
 $errors[] = new Error('username', 'Username does not exist.');
 }
 }
 return $errors;
 }
}
?>< /p>

Error is a class written by myself:

/**
 * Validation error.
*/
final class Error {
 private $source;
 private $message;< /p>

 /**
     * Create new error.
     * @param mixed $source source of the error
     * @param string $message error message
*/
 function __construct($source, $message) {
 $this->source = $source;
 $this->message = $message;
 }
 /**
     * Get source of the error.
     * @return mixed source of the error
*/
 public function getSource() {
 return $this->source;
 }
 /* *
     * Get error message.
     * @return string error message
*/
 public function getMessage() {
 return $this->message;
 }
}
?>

2. Call the validator to proceed verify

$username = null;
$password = null;
$msg = "";
< ;p>if (isset($_POST['username']) && isset($_POST['password'])) {
 $username = addslashes(trim(stripslashes($_POST ['username'])));
 $password = addslashes(trim(stripslashes($_POST ['password'])));
 // validate
 $errors = LoginValidator::validate($username, $password);

 if (empty($errors)) {
 // save the latest ip or login time into database, then processing page forwarding
 $dao = new UserDao();
 $user = $dao->findByName($username);
 $last_login_ip = Utils::getIpAddress ();
 $user->setLastLoginIp($last_login_ip);
 $now = new DateTime();
 $user->setLastLoginTime($now);
 $dao->save($user);
 UserLogin ::setUserInfo($user);
 Flash::addFlash('Login successful!');
 Utils::redirect('welcome');
 }

 foreach ($errors as $e) {
 $msg .= $e->getMessage()."";
 }
 ?>