Question

how can I fill the two lists with corresponding elements in method fillArrayList the user must enter the values

import java.util.ArrayList;
import java.util.Scanner;

class Assignment1
{
    public static void main(String[] args)
    {
      ArrayList<Integer> list1 = new ArrayList<Integer>();
      ArrayList<Integer> list2 = new ArrayList<Integer>();

      System.out.println("Enter your lists = ");
      fillArrayList(list1,list2);

    }

    public static void fillArrayList(ArrayList<Integer> L1 ,ArrayList<Integer> L2 )
    {
           //don't know what to do here to fill two lists from the user , really need help

    }

Answer 1

I think you should modify your fillArrayList signature to just fill one list at a time. And you can invoke it twice for your two arraylist.

So, your method should be like: –

public static void fillArrayList(ArrayList<Integer> myList) {
    /* Let the code be same as the one in @AmitD's post */

    Scanner scanner = new Scanner(System.in);
    System.out.println("Enter elemetns for List: Enter -1 to end ");

    while (scanner.hasNext()) {
        if (scanner.hasNextInt()) {
            int i = scanner.nextInt();
            if (i == -1)
                break;

            myList.add(i);
        } else {
            System.out.println("Invalid value Please enter integer");
            scanner.next();
        }
    }

}

Then declare your two lists as instance variable, outside the main method. And use List for reference type.

List<Integer> list1 = new ArrayList<Integer>();
List<Integer> list2 = new ArrayList<Integer>();

Now, from the main method, you can invoke this method twice for each list like this: –

fillArrayList(list1);
fillArrayList(list2);

And back in your main method, you can print your list, as the change you do in fillArrayList method will get reflected there also.

System.out.println(list1);
System.out.println(list2);