package  a6;

public class ListHead {

    public ListHead next;
    public ListHead prev;
    public Object data;

    public ListHead() {
        next = this;
        prev = this;
    }

    public void del() {

    }

    public void delInit() {

    }

    public void addTail(ListHead newNode) {

    }

    public Object firstEntry() {
        return next.data;
    }

    public void replace(ListHead pnew) {
        pnew.next = next;
        pnew.next.prev = pnew;
        pnew.prev = prev;
        pnew.prev.next = pnew;
        pnew.data = data;
    }

    public void replaceInit(ListHead pnew) {
        replace(pnew);
        init();
    }

    public boolean empty() {
        return next == this;
    }

    public void init() {

    }

}