public void displayList() {
SLink current = first;
if (isEmpty()) {
System.out.println("list is empty.");
return;
}
while (current.next != null) {
current.displayLink();
System.out.println("");
current = current.next;
}
}
public void insertFirst(int data) {
SLink slink = new SLink(data);
if (isEmpty()) first = slink;
slink.next = first;
first = slink;
}