Java Data Structures Linked List

class Link {/*from  ww w.j a  v a 2 s  .c  o  m*/
   public int id; // data item
   public double data; // data item
   public Link next; // next link in list

   public Link(int id, double dd) // constructor
   {
      this.id = id; // initialize data
      data = dd; // ('next' is automatically // set to null)
   } 

   public void displayLink() // display ourself
   {
      System.out.print("{" + id + ", " + data + "} ");
   }
}

class LinkList {
   private Link first; // ref to first link on list

   public LinkList() {
      first = null; // no links on list yet
   }

   public boolean isEmpty(){
      return (first == null);
   }
   // insert at start of list
   public void insertFirst(int id, double dd) {
      Link newLink = new Link(id, dd);
      newLink.next = first;
      first = newLink;
   }

   public Link deleteFirst() // delete first item
   {
      Link temp = first;
      first = first.next;
      return temp;
   }

   public void displayList() {
      System.out.print("List (first-->last): ");
      Link current = first; // start at beginning of list
      while (current != null) // until end of list,
      {
         current.displayLink(); // print data
         current = current.next; // move to next link
      }
      System.out.println("");
   }
}

public class Main {
   public static void main(String[] args) {
      LinkList theList = new LinkList();

      theList.insertFirst(2, 2.99);
      theList.insertFirst(4, 4.99);
      theList.insertFirst(6, 6.99);
      theList.insertFirst(8, 8.99);

      theList.displayList();

      while (!theList.isEmpty()) {
         Link aLink = theList.deleteFirst();
         System.out.print("Deleted ");
         aLink.displayLink();
         System.out.println("");
      }
      theList.displayList();
   }
}