Question

我是PHP的新手。我现在学习可见范围概念（也称为访问修饰符）。

我在这个论坛上也阅读了以下两个链接：

Failed to get an object property that containing ":protected"

What is the difference between public, private, and protected?

我在一个名为＆＃34; class.Address.inc＆＃34;的文件中创建了一个简单的类：

<?php

/**
 * Physical address. 
 */
class Address {
  // Street address.
  public $street_address_1;
  public $street_address_2;

  // Name of the City.
  public $city_name;

  // Name of the subdivison.
  public $subdivision_name;

  // Postal code.
  public $postal_code;

  // Name of the Country.
  public $country_name;

  // Primary key of an Address.
  protected $_address_id;

  // When the record was created and last updated.
  protected $_time_created;
  protected $_time_updated;

  /**
   * Display an address in HTML.
   * @return string 
   */
  function display() {
    $output = '';

    // Street address.
    $output .= $this->street_address_1;
    if ($this->street_address_2) {
      $output .= '<br/>' . $this->street_address_2;
    }

    // City, Subdivision Postal.
    $output .= '<br/>';
    $output .= $this->city_name . ', ' . $this->subdivision_name;
    $output .= ' ' . $this->postal_code;

    // Country.
    $output .= '<br/>';
    $output .= $this->country_name;

    return $output;
  }
}

然后，我在demo.php文件中创建了一个简单的程序，如下所示：

require 'class.Address.inc';

echo '<h2>Instantiating Address</h2>';
$address = new Address;

echo '<h2>Empty Address</h2>';
echo '<tt><pre>' . var_export($address, TRUE) . '</pre></tt>';

echo '<h2>Setting properties...</h2>';
$address->street_address_1 = '555 Fake Street';
$address->city_name = 'Townsville';
$address->subdivision_name = 'State';
$address->postal_code = '12345';
$address->country_name = 'United States of America';
echo '<tt><pre>' . var_export($address, TRUE) . '</pre></tt>';

echo '<h2>Displaying address...</h2>';
echo $address->display();

echo '<h2>Testing protected access.</h2>';
echo "Address ID: {$address->_address_id}";

除了最后一行之外，所有内容都适用于上述程序。我收到一个致命错误，说我无法访问＆＃34; _address_id属性＆＃34;。为什么呢？

受保护的范围是指您希望在扩展当前类（包括父类）的所有类中显示变量/函数。

＆＃34; $地址＆＃34; object来自当前名为Address的类。那么我做错了什么？

请协助。

的Qwerty

Answer 1

尝试访问受保护属性的代码必须位于类的方法或扩展它的类中。您询问的echo行不在任何类方法中，而是在脚本的全局代码中。在课堂外看不到受保护的属性和私有属性。

为什么我不能直接从自己的类访问受保护的属性？

1 个答案: