title: Do we need the previous element in a linked list?
body: <p>In the implementation of <code>HashMap</code>, linked lists are used to represent elements in buckets.
  Each Entry has a element to the next Entry. See: <a href="http://grepcode.com/file/repository.grepcode.com/java/root/jdk/openjdk/6-b14/java/util/HashMap.java#HashMap.remove%28java.lang.Object%29" rel="nofollow">Ref</a>.  However, in the implementation for the <code>LinkedList</code> class, each element has a reference to its previous element and its next element see <a href="http://grepcode.com/file/repository.grepcode.com/java/root/jdk/openjdk/6-b14/java/util/LinkedList.java" rel="nofollow">Ref</a>.  Just trying to figure out why <code>previous</code> is important in one linked list and not another?</p>