Java – How to convert a primitive Array to List

Java – How to convert a primitive Array to List

Code snippets to convert a primitive array int[] to a List<Integer> :

 int[] number = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};

 List<Integer> list = new ArrayList<>();
 for (int i : number) {
     list.add(i);
 }

In Java 8, you can use the Stream APIs to do the boxing and conversion like this :

 List<Integer> list = Arrays.stream(number).boxed().collect(Collectors.toList());

1. Classic Example

Full example to convert a primitive Array to a List.ArrayExample1.java

package com.mkyong.array;

import java.util.ArrayList;
import java.util.List;

public class ArrayExample1 {

    public static void main(String[] args) {

        int[] number = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};

        List<Integer> list = convertIntArrayToList(number);
        System.out.println("list : " + list);

    }

    private static List<Integer> convertIntArrayToList(int[] input) {

        List<Integer> list = new ArrayList<>();
        for (int i : input) {
            list.add(i);
        }
        return list;

    }
}

Output

list : [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

Note
You can’t use the popular Arrays.asList to convert it directly, because boxing issue.

 int[] number = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
 // No, the return type is not what we want
 List<int[]> ints = Arrays.asList(number);

2. Java 8 Stream

Full Java 8 stream example to convert a primitive Array to a List.ArrayExample2.java

package com.mkyong.array;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.IntStream;

public class ArrayExample2 {

    public static void main(String[] args) {

        int[] number = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};

        // IntStream.of or Arrays.stream, same output
        //List<Integer> list = IntStream.of(number).boxed().collect(Collectors.toList());
 
        List<Integer> list = Arrays.stream(number).boxed().collect(Collectors.toList());
        System.out.println("list : " + list);

    }
}

Output

list : [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

References

  1. IntStream JavaDoc
  2. Java – Convert Array to Stream

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