php单例模式的原理及实现方法

<?php
/**
 * @copyright 2013 maguowei.com
 * @author Ma Guowei <imaguowei@gmail.com>
 */
/**
 * 单例模式
 * Class Single
 */
class Single
{
  private $name;
  private static $single;
  private function __construct()
  {
  }
  public static function init()
  {
    if(empty(self::$single))
    {
      self::$single = new Single();
    }
    return self::$single;
  }
  public function getName()
  {
    return $this->name;
  }
  public function setName($name)
  {
    $this->name = $name;
  }
}
$s = Single::init();
$s->setName(&#39;hhhh&#39;);
echo &#39;$s:&#39;.$s->getName();
unset($s);
$m = Single::init();
echo &#39;$m:&#39;.$m->getName();