$re = '/(?<=\n|\A)(?:public\s)?(class|interface|enum)\s([^\n\s]*)/six';
$str = '/**
*
* @author XXXX
* Introduction: A common interface that judges all kinds of algorithm tags.
* some other comment
*/
public class TagMatchingInterface
{
// content
public class InnerClazz{
// content
}
}';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php