Avoiding inheritance, how could I give my class a default creation dependency?

Say I have a class:

use App/Jedi;
use App/Interfaces/Teacher;   // <-- Jedi is an implementation of Teacher

class AnakinSkywalker implements Apprenticeable;
{
    private $teacher;
    public $lightSaberColor = "blue";

    public function __construct(Jedi $teacher){  // <-- default Teacher
        $this->setTeacher($teacher);         
    }        

    public function setTeacher(Teacher $teacher){  // <-- can change later here
         $this->teacher = $teacher; 
    }

    public function printHowManyCanTeach(){
        echo $teacher->count();
    }

    // ...
}

Lots of places in my app I use it like this:

$character = new AnakinSkywalker;
echo $character->howManyCanTeach();    // prints "Many masters"
...

But one day I decide somewhere specific in my app I need to do this instead:

$sith = new Sith;   // <-- Sith is an implementation of Teacher
$characher = (new AnakinSkywalker)->setTeacher($sith);
echo $character->howManyCanTeach();  // prints "Always two there are, no more, no less"
...

Is this a proper, loosely coupled solution to give an object a default dependency with the ability to change it out later? If not, why, and what could I do to accomplish this?