title: Set.of vs Collections.singleton
body: <p>Since the immutable implementation of <code>Set.of(E e)</code> has been introduced in <code>Java 9</code>, do we still need to use <code>Collections.singleton(E e)</code>? What would be the use case for the latter one? </p>
  
  <p>It doesn't seem to be obvious from looking at the source code of both implementations. I don't see any significant difference except that <code>Set12</code> implementation explicitly denies deserialisation.</p>
  
  <p>I would personally go for <code>Set.of(...)</code> for the all new code at least because of the stylish point of view (a shorter code, less imports). But may be I am missing some crucial point?</p>