Linked Lists - Advanced Topics in Java: Core Concepts in Data Structures - page 87

But if we need a list of characters, we would need to change the heading to this:
public void addHead(char c)
and, for a list of Part objects, to this:
public void addHead(Part p)
If there are many methods in the class, these changes could become quite tedious every time we need to change
the kind of data stored in our list.
We will use an approach that will minimize the changes required in LinkedList .
Let's define the class Node as follows:
class Node {
NodeData data;
Node next;
public Node(NodeData nd) {
data = nd;
next = null;
}
} //end class Node
We write the class in terms of an unspecified, as yet, data type, NodeData . There are two fields, data and next .
Without knowing anything more about NodeData , we can write addHead as follows:
public void addHead(NodeData nd) {
Node p = new Node(nd);
p.next = head;
head = p;
}
A class ( TestList , say) that wants to use LinkedList must provide a definition of NodeData that is available to
LinkedList . Suppose we want a linked list of integers. We can define NodeData as follows (we will explain the need for
toString shortly):
public class NodeData {
int num;
public NodeData(int n) {
num = n;
}
public String toString() {
return num + " ";
//" " needed to convert num to a string; may also use "" (empty string)
}
} //end class NodeData