How to auto load file class in PHP

Here's the sample how to load class in the file of PHP
here we go! Let's put two files in the html(/var/www/html) directory on your computer.
First file contain of Class code:
# sample.php

< ?php

class Sample
{
    // property declaration
    public $var = 'hello world';

    // method declaration
    public function display() {
        echo $this->var;
    }
}

? >

Second file:
# load.php

< ?php

function __autoload($class_name) {
    include strtolower($class_name) . '.php';
}

$obj  = new Sample();

echo $obj->display();

? >

Next step is access load.php file from localhost:
http://localhost/load.php for more visit this page