title: HashSet vs LinkedHashSet
body: <p>What is the difference between them? I know that </p>
  
  <blockquote>
    <p>A LinkedHashSet is an ordered version of HashSet that
    maintains a doubly-linked List across all elements. Use this class instead of HashSet
    when you care about the iteration order. When you iterate through a HashSet the
    order is unpredictable, while a LinkedHashSet lets you iterate through the elements
    in the order in which they were inserted. </p>
  </blockquote>
  
  <p>But in sourcecode of LinkedHashSet there are only calling constructors of HashSet. So where is double-linked List and insertion order?</p>