How to create our own LinkedList implemenatation in java ?

1)LinkedList.java

package llist;
import java.util.NoSuchElementException;

/**
   A linked list is a sequence of nodes with efficient
   element insertion and removal. This class
   contains a subset of the methods of the standard
   java.util.LinkedList class.
*/
public class LinkedList
{ 
   private Node first;
  
   /**
      Constructs an empty linked list.
   */
   public LinkedList()
   { 
      first = null;
   }
  
   /**
      Returns the first element in the linked list.
      @return the first element in the linked list
   */
   public Object getFirst()
   { 
      if (first == null) { throw new NoSuchElementException(); }
      return first.data;
   }

   /**
      Removes the first element in the linked list.
      @return the removed element
   */
   public Object removeFirst()
   { 
      if (first == null) { throw new NoSuchElementException(); }
      Object element = first.data;
      first = first.next;
      return element;
   }

   /**
      Adds an element to the front of the linked list.
      @param element the element to add
   */
   public void addFirst(Object element)
   { 
      Node newNode = new Node();
      newNode.data = element;
      newNode.next = first;
      first = newNode;
   }
  
   /**
      Returns an iterator for iterating through this list.
      @return an iterator for iterating through this list
   */
   public ListIterator listIterator()
   { 
      return new LinkedListIterator();
   }
  
   class Node
   { 
      public Object data;
      public Node next;
   }

   class LinkedListIterator implements ListIterator
   { 
      private Node position;
      private Node previous;
      private boolean isAfterNext;

      /**
         Constructs an iterator that points to the front
         of the linked list.
      */
      public LinkedListIterator()
      { 
         position = null;
         previous = null;
         isAfterNext = false;
      }
     
      /**
         Moves the iterator past the next element.
         @return the traversed element
      */
      public Object next()
      { 
         if (!hasNext()) { throw new NoSuchElementException(); }
         previous = position; // Remember for remove
         isAfterNext = true;

         if (position == null)
         {
            position = first;
         }
         else
         {
            position = position.next;
         }

         return position.data;
      }
     
      /**
         Tests if there is an element after the iterator position.
         @return true if there is an element after the iterator position
      */
      public boolean hasNext()
      { 
         if (position == null)
         {
            return first != null;
         }
         else
         {
            return position.next != null;
         }
      }
     
      /**
         Adds an element before the iterator position
         and moves the iterator past the inserted element.
         @param element the element to add
      */
      public void add(Object element)
      { 
         if (position == null)
         {
            addFirst(element);
            position = first;
         }
         else
         { 
            Node newNode = new Node();
            newNode.data = element;
            newNode.next = position.next;
            position.next = newNode;
            position = newNode;
         }

         isAfterNext = false;
      }
     
      /**
         Removes the last traversed element. This method may
         only be called after a call to the next() method.
      */
      public void remove()
      { 
         if (!isAfterNext) { throw new IllegalStateException(); }

         if (position == first)
         {
            removeFirst();
         }
         else
         { 
            previous.next = position.next;
         }
         position = previous;
         isAfterNext = false;
      }

      /**
         Sets the last traversed element to a different value.
         @param element the element to set
      */
      public void set(Object element)
      {
         if (!isAfterNext) { throw new IllegalStateException(); }
         position.data = element;
      }
   }
}


2)ListIterator.java

/**
   A list iterator allows access of a position in a linked list.   
   This interface contains a subset of the methods of the
   standard java.util.ListIterator interface. The methods for
   backward traversal are not included.
*/
package llist;
public interface ListIterator
{ 
   /**
      Moves the iterator past the next element.
      @return the traversed element
   */
   Object next();
     
   /**
      Tests if there is an element after the iterator position.
      @return true if there is an element after the iterator position
   */
   boolean hasNext();
     
   /**
      Adds an element before the iterator position
      and moves the iterator past the inserted element.
      @param element the element to add
   */
   void add(Object element);
     
   /**
      Removes the last traversed element. This method may
      only be called after a call to the next() method.
   */
   void remove();

   /**
      Sets the last traversed element to a different value.
      @param element the element to set
   */
   void set(Object element);
}


3)ListDemo.java

/**
   A program that demonstrates the LinkedList class
*/
package llist;
public class ListDemo
{ 
   public static void main(String[] args)
   { 
      LinkedList staff = new LinkedList();
      staff.addFirst("Tom");
      staff.addFirst("Romeo");
      staff.addFirst("Harry");
      staff.addFirst("Diana");
     
      // | in the comments indicates the iterator position

      ListIterator iterator = staff.listIterator(); // |DHRT
      iterator.next(); // D|HRT
      iterator.next(); // DH|RT

      // Add more elements after second element
     
      iterator.add("Juliet"); // DHJ|RT
      iterator.add("Nina"); // DHJN|RT

      iterator.next(); // DHJNR|T

      // Remove last traversed element

      iterator.remove(); // DHJN|T
    
      // Print all elements

      iterator = staff.listIterator();
      while (iterator.hasNext())
      {
         System.out.print(iterator.next() + " ");
      }
      System.out.println();
   }
}