code: public Entry insertAtBottom(Entry entry)
    {
      if (tc.isEntryEnabled())
        SibTr.entry(tc, "insertAtBottom", new Object[] { entry });
  
      //only add in the new entry if it is not already in a list.
      if(entry.parentList == null)
      {
        //if the list is empty
        if(last == null)
        {
          //double check that the link references are null
          entry.previous = null;
          entry.next = null;
          //record the first and last pointers
          first = entry;
          last = entry;
          //set the entry's parent list to show that it is now part of this list
          entry.parentList = this;
        }
        else //if there are already entries in the list
        {
          //insert the new entry after the last one in the list
          insertAfter(entry, last);        
        }            
                   
        if (tc.isEntryEnabled())
          SibTr.exit(tc, "insertAtBottom", entry);
      
        return entry;
      }
      
      //if the entry is already in a list, throw a runtime exception
      SIErrorException e = new SIErrorException(
        nls.getFormattedMessage(
          "INTERNAL_MESSAGING_ERROR_CWSIP0001",
          new Object[] {
            "com.ibm.ws.sib.processor.utils.linkedlist.LinkedList",
            "1:166:1.18" },
          null));
            
      FFDCFilter.processException(
        e,
        "com.ibm.ws.sib.processor.utils.linkedlist.LinkedList.insertAtBottom",
        "1:172:1.18",
        this);
              
      SibTr.exception(tc, e);   
      SibTr.error(tc, "INTERNAL_MESSAGING_ERROR_CWSIP0001",
      new Object[] {
        "com.ibm.ws.sib.processor.utils.linkedlist.LinkedList",
        "1:179:1.18" });   
      
      if (tc.isEntryEnabled())
        SibTr.exit(tc, "insertAtBottom", e);
            
      throw e;
    }
docs: Synchronized. Insert a new entry in to the list at the bottom.
  The new entry must not be already in any list, including this one.
  
  @param entry The entry to be added.
  @return The entry after it has been added