public class Singleton
{
  private volatile static Singleton instance = null;

  private Singleton ()
  {
  }

  public static Singleton getInstance ()
  {
    Singleton result = instance;
    if (result == null)
    {
      synchronized (Singleton.class)
      {
        result = instance;
        if (result == null) {
          instance = result = new Singleton ();
        }
      }
    }
    return result;
  }
}