title: Singleton classes
body: <p>Is there any difference between a Singleton class and a class with
  all static members (i.e. methods and attributes).</p>
  
  <p>I could not find any instance where 'all static member class' would not achieve
  the same functionality as class properly implementing Singleton pattern?</p>
  
  <p>For eg. <code>java.lang.Runtime</code> is a proper Singleton class whereas java.lang.System has all static method for access and merely has a private constructor to avoid external construction . Does anybody know why classes like <code>Runtime</code> are made <code>Singleton</code> and not implemented like <code>java.lang.System</code>.</p>
  
  <p>Is it merely because it would be a cleaner design (i.e. mimics an object more realistically) or is there some performance benefit here?</p>