The solution is already passing. However, I cannot understand the line "public static ArrayList<String> doubleValues(ArrayList<String> list)". How does it work and what is it for. Can you please explain this in detail? 
package com.codegym.task.task07.task0717;

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.ArrayList;

/*
Duplicating words

*/

public class Solution {
   public static void main(String[] args) throws Exception {

    	BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));

    	ArrayList <String> list = new ArrayList<String>();

    	for(int i =0; i < 10; i++) {

        	list.add(reader.readLine());
        }

    	ArrayList<String> result = doubleValues(list);

        for(String s : result) {
        	System.out.println(s);
        }
    }

    public static ArrayList<String> doubleValues(ArrayList<String> list) {


    	for(int i = 0; i < list.size(); i++) {

    		if(true) {
    		list.add(i+1, list.get(i));
    		i++;
    		}

    	}
        return list;
    }
}