// ListNode is a class for storing a single node of a linked list.  This      
// node class is for a list of integer values.     
 
public class ListNode {                  
    public int data;       // data stored in this node                           
    public ListNode next;  // link to next node in the list            
         
    // post: constructs a node with data 0 and null link              
    public ListNode() {           
        this(0, null);     // this.data = 0;     
    }                      // this.next = null;    
                           
    // post: constructs a node with given data and null link            
    public ListNode(int data) {         
        this(data, null);  // this.data = data;                   
    }                      // this.next = null;                    
                   
    // post: constructs a node with given data and given link                           
    public ListNode(int data, ListNode next) {              
        this.data = data;               
        this.next = next;               
    }  
}