Linked Lists - Building Java Programs: A Back to Basics Approach - page 937

You can use any variable name you like, although it is common in linked list pro-
gramming to use a name like current or curr . The preceding line of code initializes
current to point to the same value as list (the first node in the list):

data
3

next data

5

next data

2

next
/

list

current

You want a loop that prints the various values, and you want it to keep going as long
as there is more data to print. So how do you structure your loop? The variable current
will refer to each different node in turn. The final node has the value null in its next
field, so eventually the variable current will become equal to null and that's when
you know your loop is finished. Thus, your basic loop structure will be as follows:

ListNode current = list;
while (current != null) {
process next value.
move current forward.

}

To process a node, you need to print out its value, which you can get from
current.data , and you need to move current to the next node over. The position
of the next node is stored in current.next , so moving to that next node involves
resetting current to current.next :

ListNode current = list;
while (current != null) {
System.out.println(current.data);
current = current.next;

}

The first time through this loop, current is referring to the node with the 3 in it.
It prints this value and then resets current , which causes current to refer to (or
point to) the second node in the list:

data
3

next data

5

next data

2

next
/

list

current

Some people prefer to visualize this differently. Instead of envisioning the variable
current sitting still while its arrow moves, some people prefer to envision the vari-
able itself moving. So, for the initial situation, you draw the following picture: