how to convert an Array to a linked list in Java

Question

I am a fairly new Java programmer and I am currently learning about converting lists to arrays. The problem that I am having is that when I try to link the list the output I am getting is not the same as what is in the array. The linked list output is all null values while the array has random values as it should. Here is my code:

import java.util.Arrays;
import java.util.LinkedList;
import java.util.List;

public class InsertingElements {
    public static void main(String[] args) {
        Integer[] numbers = new Integer[25];
        List<Integer> linkList = new LinkedList<>(Arrays.asList(numbers));

        for (int i = 0; i < numbers.length; i++) {
            numbers[i] = (int) (Math.random() * 100 + 1);
        }

        System.out.println("Numbers Generated: " + Arrays.toString(numbers));

        numbers = linkList.toArray(new Integer[linkList.size()]);

        System.out.println("Numbers: ");
        for (Integer number : numbers) {
            System.out.println(number);
        }
    }
}

And here is the output:

Numbers Generated: [92, 61, 25, 8, 48, 80, 85, 89, 53, 18, 48, 38, 48, 
41, 93, 94, 24, 73, 83, 21, 18, 52, 3, 14, 10]
Numbers: 
null
null
null
null
null
null
null
null
null
null
null
null
null
null
null
null
null
null
null
null
null
null
null
null
null

cbaldan · Accepted Answer · 2018-11-15 00:17:36Z

16

Move List<Integer> linkList = new LinkedList<> (Arrays.asList(numbers)); to after where you populate the array otherwise your linked list is just a list of default values.

edited Nov 15, 2018 at 0:17

cbaldan

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answered Sep 6, 2018 at 3:37

John3136

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2 Comments

FiReTiTi Over a year ago

This does not work on Java 11. Wee need to use: new LinkedList<>(Arrays.asList(ArrayUtils.toObject(nums)))

Makc Over a year ago

@FiReTiTi It works, take a closer look, numbers is Integer[] not an int[], and all what ArrayUtils from Apache Commons does is "boxing" - converting from int[] to Integer[]

AbdusSalam · Accepted Answer · 2018-09-06 03:53:09Z

Try this one

import java.util.Arrays;
import java.util.LinkedList;
import java.util.List;

    public class InsertingElements {
        public static void main(String[] args) {
            Integer[] numbers = new Integer[25];

            for (int i = 0; i < numbers.length; i++) {
            numbers[i] = (int) (Math.random() * 100 + 1);
           }

           List<Integer> linkList = new LinkedList<>(Arrays.asList(numbers));
           System.out.println("Numbers Generated: " + Arrays.toString(numbers));

          numbers = linkList.toArray(new Integer[linkList.size()]);

          System.out.println("Numbers: ");
          for (Integer number : numbers) {
          System.out.println(number);
        }
      }
    }

GiGaNtIc BuRgEr · Accepted Answer · 2020-11-01 03:39:44Z

0

import java.util.Arrays;
import java.util.LinkedList;
import java.util.List;

    public class InsertingElements {
        public static void main(String[] args) {
            Integer[] numbers = new Integer[25];

            for (int i = 0; i < numbers.length; i++) {
            numbers[i] = (int) (Math.random() * 100 + 1);
           }

           List<Integer> linkList = new LinkedList<>(Arrays.asList(numbers));
           System.out.println("Numbers Generated: " + Arrays.toString(numbers));

          numbers = linkList.toArray(new Integer[linkList.size()]);

          System.out.println("Numbers: ");
          for (Integer number : numbers) {
          System.out.println(number);
        }
      }
    }

answered Nov 1, 2020 at 3:39

GiGaNtIc BuRgEr

12 bronze badges

1 Comment

Prashanth Debbadwar Over a year ago

Just an FYI. When we create a list using a constructor that accepts an array, the list internally iterates the array and adds elements to the list. The list object doesn't hold the reference of the array once the constructor block is executed. That's why @michael 's code is not working.

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