有序链表

　　其实就是重写insert()方法，添加时进行一段比较。因为是泛型，利用到Comparable类的compareTo()方法。

public class SortedSinglyList<T extends Comparable<? super T>> extends SinglyList<T> {
    public SortedSinglyList() {
        super();
    }
    
    public Node<T> insert(T x){
        Node<T> p = head.next;
        Node<T> front = head;
        
        while(p != null && x.compareTo(p.data) > 0){
                front = p;
                p = p.next;
        }
        front.next = new Node<T>(x,p);
        16         return front.next;
    }
}