Linked Data Structures - Absolute Java - page 841

Internally, the local variable position references the current node in the linked list,
whereas the local variable previous references the node linking to the current node.
The purpose of the previous variable will be seen when adding and deleting nodes. In
the constructor and the restart( ) method, position is set to head and previous
is set to null .
To determine if the end of the list has been reached, hasNext( ) returns whether
or not position is null :
return (position != null );
To step through the list, the next( ) method first throws an exception if we have
reached the end of the list:
if (!hasNext( ))
throw new NoSuchElementException( );
Otherwise, the method retrieves the string value of the iterator referenced by position
in the variable toReturn , advances previous to reference the current position,
advances position to the next node in the list, and returns the string:
String toReturn = position.item;
previous = position;
position = position.link;
return toReturn;
The definition of the method changeHere is left to Self-Test Exercise 13. (If
necessary, you can look up the definition in the answer to Self-Test Exercise 13.) The
techniques for adding and deleting nodes are discussed in the next subsection.
The Java Iterator Interface
Java has an interface named Iterator that specifies how Java would like an iterator to
behave. It is in the package java.util (and so requires that you import this package). Our
iterators do not quite satisfy this interface, but they are in the same general spirit as that
interface and could be easily redefined to satisfy the Iterator interface.
The Iterator interface is discussed in Chapter 16.
Adding and Deleting Nodes
To add or delete a node in a linked list, you normally use an iterator and add or delete
a node at the (approximate) location of the iterator. Because deleting is a little easier
than adding a node, we will discuss deleting first.