Constructor:


PHP 5 allows developers to declare constructor methods for classes.Classes call constructor method on each newly-created object. 
function __construct() {
//
}
Example:


<?php
class MainClass {
   function __construct() {
      echo "In MainClass constructor\n";
   }
}


class ChildClass extends MainClass {
   function __construct() {
       parent::__construct();
      echo "In SubClass constructor\n";
   }
}


$obj = new MainClass();
$obj = new SubClass();
?>
Note: If  PHP 5 cannot find a __construct() function for a given class, it will search for the old constructor function, by the name of the class. 


Destructor:


The destructor method will be called as soon as Classes destroy the object.


 function __destruct() {
  //     
   }
Example:


<?php
class MainClass {
   function __construct() {
      echo "In MainClass constructor\n";
   }
function __destruct() {
       print "Destroying \n";
   }
}
class ChildClass extends MainClass {
   function __construct() {
       parent::__construct();
      echo "In SubClass constructor\n";
   }
   
}


$obj = new MainClass();
$obj = new SubClass();
?>


Note:The destructor method will be called even if script execution is stopped using exit().