Main.java使用未经检查或不安全的操作

Question

I tried to implement my own singly linkedList in java and I wanted it to be generic because I think it's the best choice. Then, I want to write a specific function to sum two linkedlist of integer. The problem is due to the genericity of the list, I got an error and I can't check my code...

Here is the code of my function :

public LinkedList<Integer> sum(LinkedList<Integer> list1, LinkedList<Integer> list2){
//  if (list1== null || list2 ==null) return null;

    LinkedList<Integer> result = new LinkedList<Integer>();

    Node<Integer> node11 = list1.first;
    Node<Integer> node22 = list2.first;
    int temp = 0;

    while (node11.next!=null && node22.next!=null){
            int node1 = node11.data;
            int node2 = node22.data;
            int node3 = (node1 + node2 + temp) %10;
            temp = (node1 + node2)>=10 ? 1: 0;
            result.insertLast(node3);

            node11 = node11.next;
            node22 = node22.next;
    }

    return result;

             }

There is the code for my two classes : Node and linkedList

class Node<T> {
  public T data;                // data in Node.
  public Node<T> next;          // points to next Node in list.

  public Node(T data){                                       
  this.data = data;
  }
}

class LinkedList<T> {
public Node<T> first;       

public LinkedList(){
      first = null;
}

 public void insertLast(T data){
      Node<T>  newNode = new Node<T> (data);        //Creation of New Node.

      if(first==null)   {
             first=newNode;                 
             return;
      }

      Node<T>  tempNode = first;
            while(tempNode.next!=null){
            tempNode=tempNode.next;
            }
      tempNode.next=newNode; 
      }

And here is my main when I wanted to try this code :

    LinkedList<Integer> list = new LinkedList();
    LinkedList<Integer> list2 = new LinkedList();

    list.insertLast(5);
    list.insertLast(1);
    list.insertLast(3);    

    list2.insertLast(2);
    list2.insertLast(9);
    list2.insertLast(5); 

    LinkedList<Integer> list3 = sum(list, list2);

And there is the error that I get (i'm using ideone as an IDE) :

     Main.java:179: error: cannot find symbol
    LinkedList<Integer> list3 = sum(list, list2);
                                ^
     symbol:   method sum(LinkedList<Integer>,LinkedList<Integer>)
     location: class Ideone
     Note: Main.java uses unchecked or unsafe operations.
     Note: Recompile with -Xlint:unchecked for details.

Can you please tell me where is the error and what I should do to correct that? I know it's due to genericity (because I had to only use Integer in my function). I tried a looot of things but none of them worked...

Thanks!

Answer 1

Use the keywork static in your sum method :

public static LinkedList sum(LinkedList list1, LinkedList list2){ ... }

if you call sum from static main method

Answer 2

It looks like you are adding two big integers, each is represented by a list.

There are two errors: a). in function "sum", the termination condition of while loop is incorrect. The last two elements are always not added. b). in function "sum" temp represents whether there's an increase to the previous position. It's not handled.

Consider BigInteger or java built-in List?

Answer 3

public class ThreadingMulti {
    public static void main(String[] args) throws InterruptedException {
        LinkedList<Integer> list = new LinkedList();
        LinkedList<Integer> list2 = new LinkedList();

        list.add(5);
        list.add(1);
        list.add(3);    

        list2.add(2);
        list2.add(9);
        list2.add(5); 

        LinkedList<Integer> list3 = sum(list, list2);
    }

    public static LinkedList<Integer> sum(LinkedList<Integer> list1, LinkedList<Integer> list2){
        LinkedList<Integer> result = new LinkedList<Integer>();
        return result;

    }
}

This code is working fine. Seems problem with sum method type (static). Please verify whether you might be calling non static method from static method.