是否有更短的方法来指定要运行的类？

Normally, I would have to do:

$str = "classname"; //classname is the name of a class

switch($str)
{
  case "class1":
    class1::run(); break;
  case "class2":
    class2::run(); break;
  case "class3":
    class3::run(); break;
  case "class4":
    class4::run(); break;
  case "classname":
    classname::run(); break;
  default:
    die("Fatal error: no such class");
}
//in my case, there are hundreds of cases and more being added

Is there a way of simplifying this, perhaps in one line? Wishful thinking?

$str::run()

Of course, it would be my responsibility to make sure $str is actually the name of an object. But managing that would be much easier than managing a huge list like above.

Is this possible?

Yes; as you guessed, $str::run(); works.

php> class A { public static function run() { echo "A!"; } }

php> class B { public static function run() { echo "B!"; } }

php> $n = "A";

php> $n::run();
A!
php> $n = "B";

php> $n::run();
B!

you could do something like:

if (class_exists($str) && method_exists($str,'run')){
  {$tr}::run();
}