PHP method to implement C# copycat ArrayList, _PHP tutorial

class ArrayList
{
 public $length;
 public $name;
 public $my_array;
 function __construct()
 {
  $this->my_array=Array();
 }
 public function Add($element)
 {
  array_push($this->my_array, $element);
 }
 public function get_Length()
 {
  $this->length=count($this->my_array);
  return $this->length;
 }
 public function get_Element($key)
 {
  if(array_key_exists($key, $this->my_array))
  {
   echo $this->my_array[$key];
  }
  else
  {
   echo "没有这个元素";
  }
 }
 public function list_array()
 {
  foreach ($this->my_array as $value) 
  {
   echo $value;
   echo "<br/>";
  }
 }
 public function Delete($key)
 {
  if(array_key_exists($key, $this->my_array))
  {
   $this->my_array[$key]=null;
  }
  else
  {
   echo "没有这个元素";
  }
 }
 public function erase_number()
 {
  $pattern="/[0-9]/";
  foreach ($this->my_array as $value)
  {
   if(eregi($pattern, $value))
   {
    $value=null;
   }
  }
  foreach ($this->my_array as $value) 
  {
   echo $value;
   echo "<br/>";
  }
 }
 public function erase_char()
 {
  $pattern='/a-zA-Z/';
  for($i=0;$i<count($this->my_array)-1;$i++)
  {
   if(eregi($pattern, $this->my_array[$i]))
   {
    $this->my_array[$i]=null;
   }
  }
  foreach ($this->my_array as $value) 
  {
   echo $value;
   echo "<br/>";
  }
 }
}