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。我是一名初学者，我发现自己正在努力解决这个问题。

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

只需设置start到列表中的第二个元素：

start = start.nextn