Off by One?

When p points to the last Node, the loop body will execute for the last time and print that node.

  while ( p != null )
  {
    System.out.print( p + ", " );  // print the node
    p = p.getNext();        // advance the pointer
  }

Then the pointer gets a copy of what is in the next member of that Node. But that is a null so the loop will end.

It is easy to miss the last node, or to try to go too far. This is the pointer equivalent of the notorious off-by-one error.