Node.java

package rtfour;

public class Node extends ListItem {

 public Node(Object value){
 super(value);
 }

 @Override
 ListItem next() {
 return this.rightLink;
 }

 @Override
 ListItem setNext(ListItem item) {
 this.rightLink = item;
 return this.rightLink;
 }

 @Override
 ListItem previous() {
 return this.leftLink;
 }

 @Override
 ListItem setPrevious(ListItem item) {
 this.leftLink = item;
 return this.leftLink;
 }

 @Override
 int compareTo(ListItem item) {
 if(item !=null){
 return ((String) super.getValue()).compareTo((String) item.getValue());
 }
 else{
 return -1;
 }
 }
}