oop class and object

<!-- ---------1--------- -->
<?php
class Car {

  public $name;

  function set_name($n) {
    $this->name = $n;
  }
  function get_name() {
    return $this->name;
  }
}

$obj = new Car();
$obj->set_name("BMW");
echo $obj->get_name().", ";

$obj->set_name("TOYOTA");
echo $obj->get_name().", ";

$obj->set_name("Lamborgini");
echo $obj->get_name().", ";

?>

<!-- ---------2--------- -->

<?php
class Car {

  public $color;

  function set_color($color) {
    $this->color = $color;
  }
  function get_color() {
    return $this->color;
  }
}

$obj = new Car();

$obj->set_color('Red');

echo "Color: " . $obj->get_color();

$obj->set_color('Green');

echo "<br>Color: " . $obj->get_color();

$obj->set_color('Blue');

echo "<br>Color: " . $obj->get_color();
?>

<!-- ---------3--------- -->
<?php
class Student {

  public $name;

  function std_name($n) {
    $this->name = $n;
    return $this->name;
  }
}

$obj = new Student();
echo $obj->std_name("Yousuf");
?>


<!-- ---------4--------- -->
<?php
class country {
  public $name;
  public $color;

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

$c_name = new country("Bangladesh");
echo $c_name->name();
?>

<!-- ---------5--------- -->
<?php
class country {
  public $name;
  public $color;

  function __construct($name="No name") {
    $this->name = $name;
  }
  function name() {
    return $this->name;
  }
}

$c_name = new country("Bangladesh");
echo $c_name->name();
?>