静态属性| 与'this'和'self'的关系

Question

Why is a static designation requierd to make this interpret correctly? See comment in code below.

<?php

require_once 'class.database.php';

class table extends database
{   
    static protected $_args=array(); // static added here to remove error   
    function __construct()
    {
        parent::__construct();
        self::protect();
    }
    function protect()
    {
        foreach($_POST as $key => $value)
        {
            self::$_args[$key] = mysql_real_escape_string($value);
        $i++;
        }
    }

. . .

Answer 1

There are class properties and object properties. Class properties belong to the class itself, not an instance, are declared with static, and are accessed with self::. Object properties belong to an instance of the class, are declared without static, and are accessed with $this->.

You can access a class property from an object method, if you use self::. But you'll be accessing the same property that other instances access.

You can't access an object property from a static method, of course, since there's no object/instance involved.