code: public final synchronized void insertLinkBefore(Link insertLink, Link followingLink) {
          if (TraceComponent.isAnyTracingEnabled() && tc.isEntryEnabled()) {
              SibTr.entry(
                  this,
                  tc,
                  "insertLinkBefore",
                  new long[] { insertLink.getSequence(), followingLink.getSequence()});
          }
          Link prev = followingLink._getPreviousLink();
          insertLink._link(prev, followingLink, this);
          prev._setNextLink(insertLink);
          followingLink._setPreviousLink(insertLink);
          if (TraceComponent.isAnyTracingEnabled() && tc.isEntryEnabled()) {
              SibTr.exit(this, tc, "insertLinkBefore", _debugString());
          }
      }
docs: Insert the specified link into the list.
  @param insertLink link to be inserted
  @param followingLink link before which the
  insertLink is inserted.