About how PHP implements the definition and reversal function of linked lists

<?php
class Node
{
  private $Data;//节点数据
  private $Next;//下一节点
 
  public function setData($value){
    $this->Data=$value;
  }
 
  public function setNext($value){
     $this->Next=$value;
  }  
 
  public function getData(){
    return $this->Data;
  }
 
  public function getNext(){
    return $this->Next;
  }
 
  public function __construct($data,$next){
    $this->setData($data);
    $this->setNext($next);
  }
}
class LinkList
{
  private $header;//头节点
  private $size;//长度
  public function getSize()
 {
    $i=0;
    $node=$this->header;
    while($node->getNext()!=null)
    {  
  $i++;
      $node=$node->getNext();
    }
    return $i;
  }
 
  public function setHeader($value){
    $this->header=$value;
  }
 
  public function getHeader(){
    return $this->header;
  }
 
  public function __construct(){
    header("content-type:text/html; charset=utf-8");
    $this->setHeader(new Node(null,null));
  }
  /**
  *@author MzXy
  *@param $data--要添加节点的数据
  * 
  */
  public function add($data)
  {
    $node=$this->header;
    while($node->getNext()!=null)
    {
      $node=$node->getNext();
    }
    $node->setNext(new Node($data,null));
  }
   /**
  *@author MzXy
  *@param $data--要移除节点的数据
  * 
  */
  public function removeAt($data)
  {
    $node=$this->header;
    while($node->getData()!=$data)
    {
      $node=$node->getNext();
    }
    $node->setNext($node->getNext());
    $node->setData($node->getNext()->getData());
  }
   /**
  *@author MzXy
  *@param 遍历
  * 
  */
  public function get()
  {
    $node=$this->header;
    if($node->getNext()==null){
      print("数据集为空!");
      return;
    }
    while($node->getNext()!=null)
    {
      print(&#39;[&#39;.$node->getNext()->getData().&#39;] -> &#39;);
      if($node->getNext()->getNext()==null){break;}
      $node=$node->getNext();
    }
  }
   /**
  *@author MzXy
  *@param $data--要访问的节点的数据
  * @param 此方法只是演示不具有实际意义
  * 
  */
  public function getAt($data)
  {
    $node=$this->header->getNext();
  if($node->getNext()==null){
      print("数据集为空!");
      return;
    }
    while($node->getData()!=$data)
    {
      if($node->getNext()==null){break;}
      $node=$node->getNext();
    }
    return $node->getData();    
  }
   /**
  *@author MzXy
  *@param $value--需要更新的节点的原数据 --$initial---更新后的数据
  * 
  */
  public function update($initial,$value)
  {
     $node=$this->header->getNext();
 if($node->getNext()==null){
     print("数据集为空!");
      return;
    }
    while($node->getData()!=$data)
    {
      if($node->getNext()==null){break;}
      $node=$node->getNext();
    }
 $node->setData($initial);   
  }
}
$lists = new LinkList();
$lists -> add(1);
$lists -> add(2);
$lists -> get();
echo &#39;<pre class="brush:php;toolbar:false">&#39;;
print_r($lists);
echo &#39;

function ReverseList($pHead)
{
  // write code here
  if($pHead == null || $pHead->next == null){
    return $pHead;
  }
  $p = $pHead;
  $q = $pHead->next;
  $pHead->next = null;//$pHead 变为尾指针
  while($q){
    $r = $q->next;
    $q->next = $p;
    $p = $q;
    $q = $r;
  }
  return $p;
}

function ReverseList($pHead)
{
  // write code here
  if($pHead == null || $pHead->next == null){
    return $pHead;
  }
  $res = ReverseList($pHead->next);
  $pHead->next->next = $pHead;
  $pHead->next = null;
  return $res;