Linked Lists - Advanced Topics in Java: Core Concepts in Data Structures - page 88

And we can build a linked list in reverse order with code such as the following:
LinkedList LL = new LinkedList();
System.out.printf("Enter some integers ending with 0\n");
int n = in.nextInt();
while (n != 0) {
LL.addHead(new NodeData(n)); //NodeData argument required
n = in.nextInt();
}
Note that since addHead requires a NodeData argument, we must create a NodeData object with the integer n ;
this object is passed to addHead .
How can we print the items in a list? Presumably, we would like a method ( printList , say) in the LinkedList
class, which does the job. But since LinkedList does not know what NodeData might contain (and it could vary from
one run to the next), how can it print the data in a node?
The trick is to let NodeData print itself using the toString method. Here is one way to write printList :
public void printList() {
Node curr = head;
while (curr != null) {
System.out.printf("%s", curr.data); //invokes curr.data.toString()
curr = curr.next;
}
System.out.printf("\n");
} //end printList
Recall that curr.data is a NodeData object. Since we use it in a context where a string is required, Java will look
in the NodeData class for a toString method. Since it finds one, it will use it to print curr.data . The printf statement
could also have been written as follows where we call toString explicitly:
System.out.printf("%s ", curr.data.toString());
If LL is a LinkedList , the list can be printed with this statement:
LL.printList();
So far, our LinkedList class consists of the following:
public class LinkedList {
Node head = null;
public void addHead(NodeData nd) {
Node p = new Node(nd);
p.next = head;
head = p;
}
public void printList() {
Node curr = head;
while (curr != null) {
System.out.printf("%s", curr.data); //invokes curr.data.toString()
curr = curr.next;
}