php self:: Example

using-self-in-php.php

<?php
class books
{
    public static $bookId = 0;
    public function updateBookInfo($id)
    {
        self::$bookId = $id;
    }
    public function getBookId()
    {
        return self::$bookId;
    }
}
// object 1
// before update
$objBooks = new books;
$objBooks->updateBookInfo(1);
echo $objBooks->getBookId();

// object 2
$newObjBook = new books;
echo $newObjBook->getBookId();
$newObjBook->updateBookInfo(2);

// after update
echo $objBooks->getBookId();
echo $newObjBook->getBookId();