Dependency Injection example

dschool.php

class Student {
  private $studentName;
  public __construct($studentName){
    $this->studentName = $studentName;
  }
}

class School {
  private $student;
  private $schoolName;
  public __construct($schoolName, Student $student){    // Here School class is loosly coupled with Student class.
    $this->schoolName = $schoolName;
    $this->student =  $student;     
  }
}