PHP类 - 解析错误：语法错误，意外T_STRING，期待T_FUNCTION

Question

我有一个像这样的php类代码：

class Foo{
  const ERROR_CODE = '404';
  public $public_ex = 'this is public';
  private $private_ex = 'this is private!';
  protected $protected_ex = 'this should be protected'; 
  public function getErrorCode() {
    return self::ERROR_CODE;
  }
}
$foo = new Foo;
$foo_json = json_encode($foo);
echo $foo_json;

它显示：

Parse error: syntax error, unexpected T_STRING, expecting T_FUNCTION in xxx.php on line 4

我该怎么办才能让它运转？ 非常感谢你！！ ＆GT; ＆LT;