Returns a possibly parallel  Stream with this collection as its
 source.  It is allowable for this method to return a sequential stream.
 
This method should be overridden when the spliterator()
 method cannot return a spliterator that is  IMMUTABLE,
  CONCURRENT, or late-binding. (See spliterator()
 for details.)
 Stream over the elements in this
 collection
 @implSpec
 The default implementation creates a parallel  Stream from the
 collection's  Spliterator.
Diagram: Collection List