PHP new class instantiation

Define the class BBB and save it as BBB.php. The content is as follows:

<?php 
class BBB{
private $name;
function __construct($name){
$this->name = $name;
}
function hello() {
echo $this->name;
}
}
?>

Write a php file for testing and save it as AAA.php. The content is as follows:

<?php 
require_once &#39;BBB.php&#39;;
if(class_exists(&#39;BBB&#39;)){
$bbb = new BBB(&#39;张三&#39;);
$bbb->hello();
echo "<br>";
$class = BBB;
$bbb = new $class(&#39;李四&#39;);
$bbb->hello();
echo "<br>";
$class = &#39;BBB&#39;;
$bbb = new $class(&#39;王五&#39;);
$bbb->hello();
}
?>

Access AAA.php through the browser and the output result is as follows:

Zhang San
Li Si
Wang Wu