致命错误：调用未定义的方法 User::getSkipper()

Question

我正在尝试用 PHP 自学 OOP。我有一个来自子类的错误，有人知道我为什么会收到这个错误吗？

致命错误：在第 28 行的 C:\wamp\www\starter\display.php 中调用未定义的方法 User::getSkipper()

用户类是这样的：

<?php
class User
{
    protected $_first_name;
    protected $_last_name;
    protected $_email;

    public function __construct($first_name, $last_name, $email) 
    {
        $this->_first_name = $first_name;
        $this->_last_name = $last_name;
        $this->_email = $email;
    }

    public function getFirstName()
    {
        return $this->_first_name;
    }

    public function getLastName()
    {
        return $this->_last_name;
    }

    public function getEmail()
    {
        return $this->_email;
    }       
}

?>

Skipper 类是这样的：

<?php
class Skipper extends User
{
    protected $_skipper;

    public function __construct($first_name, $last_name, $email, $skipper) 
    {
        $this->_skipper = $skipper;
    }

    public function getSkipper()
    {
        return $this->_skipper;
    }
}
?>      

执行以下代码时抛出错误：

$user1 = new User('Steven', 'Smith', 'steve@sljgksdj.com', 'Yes');
echo '<p>First Name: ' . $user1->getFirstName() .'</p>';
echo '<p>Last Name: ' . $user1->getLastName() .'</p>';
echo '<p>Email: ' . $user1->getEmail() .'</p>';
echo '<p>Skipper: ' . $user1->getSkipper() .'</p>';

Answer 1

您创建了一个 user 类的对象，而用户没有任何方法 getSkipper。 您应该创建一个 Skipper 类的对象。

$user1 = new Skipper('Steven', 'Smith', 'steve@sljgksdj.com', 'Yes');

Answer 2

如果 skipper 扩展了 User，则需要实例化 Skipper。另外，我对您通过将“是”传递给 Skipper 构造函数来实现的目标感到困惑。

<?php
class User
{
    protected $_first_name;
    protected $_last_name;
    protected $_email;

    public function __construct($first_name, $last_name, $email) 
    {
    $this->_first_name = $first_name;
    $this->_last_name = $last_name;
    $this->_email = $email;
   }

   public function getFirstName()
   {
    return $this->_first_name;
    }

    public function getLastName()
   {
    return $this->_last_name;
    }

    public function getEmail()
   {
    return $this->_email;
    }       
};

<?php
class Skipper extends User
{
protected $_skipper;

    public function __construct($first_name, $last_name, $email, $skipper) 
   {
    parent::__construct($first_name, $last_name, $email) 
    $this->_skipper = $skipper;
    }

    public function getSkipper()
    {
    return $this->_skipper;
    }
}

$skipper1 = new Skipper('Steven', 'Smith', 'steve@sljgksdj.com', 'Yes');
echo '<p>First Name: ' . $skipper1->getFirstName() .'</p>';
echo '<p>Last Name: ' . $skipper1->getLastName() .'</p>';
echo '<p>Email: ' . $skipper1->getEmail() .'</p>';