Realization of Farey sequence by single linked list

The Farey sequences of orders 1 to 8 are:

F1 = {0⁄1, 1⁄1}
F2 = {0⁄1, 1⁄2, 1⁄1}
F3 = {0⁄1, 1⁄3, 1⁄2, 2⁄3, 1⁄1}
F4 = {0⁄1, 1⁄4, 1⁄3, 1⁄2, 2⁄3, 3⁄4, 1⁄1}
F5 = {0⁄1, 1⁄5, 1⁄4, 1⁄3, 2⁄5, 1⁄2, 3⁄5, 2⁄3, 3⁄4, 4⁄5, 1⁄1}
F6 = {0⁄1, 1⁄6, 1⁄5, 1⁄4, 1⁄3, 2⁄5, 1⁄2, 3⁄5, 2⁄3, 3⁄4, 4⁄5, 5⁄6, 1⁄1}
F7 = {0⁄1, 1⁄7, 1⁄6, 1⁄5, 1⁄4, 2⁄7, 1⁄3, 2⁄5, 3⁄7, 1⁄2, 4⁄7, 3⁄5, 2⁄3, 5⁄7, 3⁄4, 4⁄5, 5⁄6, 6⁄7, 1⁄1}
F8 = {0⁄1, 1⁄8, 1⁄7, 1⁄6, 1⁄5, 1⁄4, 2⁄7, 1⁄3, 3⁄8, 2⁄5, 3⁄7, 1⁄2, 4⁄7, 3⁄5, 5⁄8, 2⁄3, 5⁄7, 3⁄4, 4⁄5, 5⁄6, 6⁄7, 7⁄8, 1⁄1}

At nth level, a new fractional a+b/c+d is inserted between two adjacent fractions A/C and b/d only when c+d<=n. The following procedure, for a given number of natural numbers n, is continuously extended to create the nth grade of the fractional list.

The data structure used is a linked list node

public class Node {
　　private int upval;//分子
　　private int dnval;//分母
　　private Node next;
　　public Node(int up, int down) {
　　　　upval = up;
　　　　dnval = down;
　　　　 next = null;
　　}
　　public Node(int up, int down, Node next) {
　　　　upval = up;
　　　　dnval = down;
　　 　　this.next = next;
　　}
　　public int getUpval() {
　　　　return upval;
　　}
　　public void setUpval(int upval) {
　　　　this.upval = upval;
　　}
　　public int getDnval() {
　　　　return dnval;
　　}
　　public void setDnval(int dnval) {
　　　　this.dnval = dnval;
　 　}
　　public Node getNext() {
　　　　return next;
　 　}
　　public void setNext(Node next) {
　　　　this.next = next;
　　}
}