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a.php
class A
{
public function __construct()
{
echo "hello world!";
}
} 
page.php
require("a.php");
$a = new A(); 
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page.php
function __autoload($classname)
{
$class_file = strtolower($classname).".php";
if (file_exists($class_file)){
require_once($class_file);
}
}
$a = new A(); 
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bool spl_autoload_register ( [callback $autoload_function] ) 
page.php
function my_own_loader($classname)
{
$class_file = strtolower($classname).".php";
if (file_exists($class_file)){
require_once($class_file);
}
}
spl_autoload_register("my_own_loader");
$a = new A(); 
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class Loader
{
public static function my_own_loader($classname)
{
$class_file = strtolower($classname).".php";
if (file_exists($class_file)){
require_once($class_file);
}
}
}
// ͨ¹ýÊý×éµÄÐÎʽ´«µÝÀàºÍ·½·¨µÄÃû³Æ
spl_autoload_register(array("my_own_loader","Loader"));
$a = new A();