从列表中删除第一项？

Question

我正在研究编程语言中指针的概念，并且我遇到了用Java编写的这个算法，我应该删除这个列表的第一项。我是初学者，我发现自己很难解决这个问题。

public class mylist {

private static class mylist
{
    public int num;
    public mylist nextn;
}

public static void main(String[] args)
{
    Scanner input = new Scanner(System.in);
    mylist start = null;
    mylist end = null;
    mylist aux;
    mylist before;
    int op, number, found;
    do{
        System.out.println("1- insert number in the beginning list");
        System.out.println("2- insert in the end of the list");
        System.out.println("3- query list");
        System.out.println("4- remove from list");  System.out.println("5- empty list");
        System.out.println("6- exit");
        System.out.print("choose: ");
        op = input.nextInt();
        if(op < 1||op>6)
        {
            System.out.println("invalid number");
        }
        if(op == 1)
        {
            System.out.println("type the number to be inserted in the beginning of the list");
            mylist newl = new mylist();
            newl.num = input.nextInt();
            if(start == null)
            {
                start = newl;
                end = newl;
                newl.nextn = null;
            }
            else
            {
                newl.nextn = start;
                start = newl;
            }
            System.out.println("number inserted");
        }
        if(op == 2)
        {
            System.out.println("type the number to be inserted in the end of the list");
            mylist newl = new mylist();
            newl.num = input.nextInt();
            if(start == null)
            {
                start = newl;
                end = newl;
                newl.nextn = null;
            }
            else
            {
                end.nextn = newl;
                end = newl;
                newl.nextn = null;
            }
            System.out.println("number inserted");
        }
        if(op == 3)
        {
            if(start == null)
            {
                System.out.println("list is empty");
            }
            else
            {  System.out.println("\nquerying the list\n");
                aux = start;
                while(aux!=null)
                {
                    System.out.print(aux.num+ " ");
                    aux = aux.nextn;

                }
            }
        }
        if(op == 4)
        {
            if(start == null)
            {
                System.out.println("list is empty");
            }
            else
            {
                System.out.println("\ntype the number to be removed:\n");
                number = input.nextInt();
                aux = start;
                before = null;
                found = 0;

                while(aux!=null)
                {
                    if(aux.num == number)
                    {
                        found = found +1;
                        if(aux == start)
                        {
                            start = aux.nextn;
                            aux = start;
                        }
                        else if(aux == end)
                        {
                            before.nextn = null;
                            end = before;
                            aux = null;
                        }
                        else
                        {
                            before.nextn =aux.nextn;
                            aux = aux.nextn;
                        }
                    }
                    else
                    {
                        before = aux;
                        aux =aux.nextn;
                    }
                }
                if(found ==0)  {
                    System.out.append("number not found");
                }
                else if(found ==1)
                {
                    System.out.append("number removed once!");
                }
                else
                {
                    System.out.append("number removed "+found+" times!");
                }
            }
        }
        if(op == 5)
        {
            if(start == null)
            {
                System.out.println("empty list");
            }
            else
            {
                start = null;
                System.out.println("emptied list");
            }
        }
    }while(op !=6);
}

}

Answer 1

只需将start设置为列表的第二个元素：

start = start.nextn