Insert node at beginning of linked list in php

Write a program which is create and add new node at the beginning of linked list in php.

Here given of code implementation process.

<?php
/*
    Php program for
    Insert node at beginning of linked list
*/
// Linked list node
class LinkNode
{
    public $data;
    public $next;
    public  function __construct($data)
    {
        $this->data = $data;
        $this->next = NULL;
    }
}
class SingleLL
{
    public $head;
    public  function __construct()
    {
        $this->head = NULL;
    }
    // Adding new node at beginning of linked list
    public  function addNode($data)
    {
        // Create new node
        $node = new LinkNode($data);
        // Connect current node to previous head
        $node->next = $this->head;
        $this->head = $node;
    }
    // Display linked list element
    public  function display()
    {
        if ($this->head == NULL)
        {
            return;
        }
        $temp = $this->head;
        // iterating linked list elements
        while ($temp != NULL)
        {
            echo(" ".$temp->data.
                " →");
            // Visit to next node
            $temp = $temp->next;
        }
        echo(" NULL\n");
    }
}

function main()
{
    $sll = new SingleLL();
    // Linked list
    // 1 → 2 → 3 → 4 → 5 → 6 → 7 → 8 → NULL
    $sll->addNode(8);
    $sll->addNode(7);
    $sll->addNode(6);
    $sll->addNode(5);
    $sll->addNode(4);
    $sll->addNode(3);
    $sll->addNode(2);
    $sll->addNode(1);
    $sll->display();
}
main();

 Linked List
 1 → 2 → 3 → 4 → 5 → 6 → 7 → 8 → NULL

Time complexity of above program is O(1).