An Introduction to Data Structures - Java Concepts - page 916

The ListIterator interface that you saw in the preceding section is a
subinterface of Iterator with additional methods (such as add and
previous ).

The compiler translates a Ȓfor eachȓ loop into an equivalent loop that uses an
iterator. The loop

for (Type variable : collection)
body

is equivalent to

Iterator<Type> iter = collection.iterator();
while (iter.hasNext())
{
Type variable = iter.next();
body
}

The ArrayList and LinkedList classes implement the Iterable interface.
If your own classes implement the Iterable interface, you can use them with
the Ȓfor eachȓ loop as wellȌsee Exercise P15.15.

15.2 Implementing Linked Lists

In the last section you saw how to use the linked list class supplied by the Java
library. In this section, we will look at the implementation of a simplified version of
this class. This shows you how the list operations manipulate the links as the list is
modified.

To keep this sample code simple, we will not implement all methods of the linked list
class. We will implement only a singly linked list, and the list class will supply direct
access only to the first list element, not the last one. Our list will not use a type
parameter. We will simply store raw Object values and insert casts w hen retrieving
them. The result will be a fully functional list class that shows how the links are
updated in the add and remove operations and how the iterator traverses the list.

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A Node object stores an object and a reference to the next node. Because the methods
of both the linked list class and the iterator class have frequent access to the Node
instance variables, we do not make the instance variables private. Instead, we make