可以在php类中创建构造函数吗？

Question

im work with php and mysql, sometimes i need instantiate my php class in data access layer for return objects, load list etc... but sometimes I use the class constructor and others do not.

Can i create doble constructor in a class?

example:

class Student {

private $id;
private $name;
private $course;

function __construct() {

}

//get set id and name

function setCourse($course) {
    $this->course = $course;
}


function getCourse() {
    $this->course = $course;
}

}

class Course {

private $id;
private $description;

function __construct($id) {
   this->id = $id;
}

//get set, id, description

}

In my access layer sometime I use the constructor in different ways for example:

        $result = $stmt->fetchAll();
        $listStudent = new ArrayObject();

        if($result != null) {

            foreach($result as $row) {

                $student = new Student();

                $student->setId($row['id']);
                $student->setName($row['name']);
                $student->setCourse(new Course($row['idcourse'])); //this works

                $listStudent ->append($sol);
            }
            }

But sometimes I need to use the constructor in another way, for example

$result = $stmt->fetchAll();
        $listCourses = new ArrayObject();

        if($result != null) {

            foreach($result as $row) {

                $course = new Course();  //but here not work, becouse Class course receives a id

                $course->setId($row['idcourse']);
                $course->setDescription($row['description']);

                $listCourses->append($sol);
            }
        }

My english is very bad, i hope you understand me

Answer 1

Use default arguments:

class Course {

  private $id;
  private $description;

  function __construct($id = 0) {
    this->id = $id;
  }

  // getters and setters for id and description

}

Now, you can use it like that:

$course = new Course(12); // works with argument

or:

$course = new Course(); // works without argument
$course->setId(12);