“类包含1个抽象方法，因此必须声明为abstract或实现其余方法（parent :: hasErrors）”[关闭]

This is my code:

interface ValidatorInterface
{
  public function hasErrors ();
  public function validate (stdClass $metadata);
  public function getFeedback ();
}

abstract class ValidatorAbstract implements ValidatorInterface
{
  protected $feedback;

  public function __construct ()
  {
    $this->feedback = new FormFeedback();
  }


  public function getFeedback ()
  {
    return $this->feedback;
  }


  public function hasErrors ()
  {
    return $this->getFeedback()->hasErrors();
  }
}

class RegistrationValidator extends ValidatorAbstract
{
  public function validate (stdClass $metadata)
  {
    $this->getFeedback()->addError('Testing');

    return !!$this->hasErrors();
  }
}

This is the error:

Fatal error: Class RegistrationValidator contains 1 abstract method and must therefore be declared abstract or implement the remaining methods (ValidatorInterface::hasErrors)

The abstract class ValidatorAbstract satisfies the requirements imposed by ValidatorInterface to have the hasErrors() and getFeedback() methods.

The class RegistrationValidator extends ValidatorAbstract and satisfies the last remaining requirement to declare a validate() method.

Why then am I getting an error saying that RegistrationValidator contains an abstract method, when it doesn't, and that it must implement hasErrors() when that method is already implemented by its parent class?