1. Introduction

In this article we will see how to convert an array i.e. primitive and object array to List. The following methods acts as a bridge between array and Collection.

Embed from Getty Images

2. How to convert array to List?

The 4 ways we are planning to convert the array to List are as follows:

1. For-each loop on array
2. Primitive stream
3. Arrays.asList
4. Stream

2.1 int[] array to List<Integer> using for-each loop

We can iterate over the array elements and insert them into the List.

int[] arr = { 1, 2, 3, 4, 5 };
List<Integer> numbers = new ArrayList<>();
for (int val : arr) {
    numbers.add(Integer.valueOf(val)); // No autoboxing
}
Assert.assertEquals(Arrays.asList(1, 2, 3, 4, 5), numbers);

2.2 int[] array to List<Integer> using IntStream

IntStream was added to Java 8 to work declaratively on int elements. Below example converts the int[] to List.

int[] arr = { 1, 2, 3, 4, 5 };
List<Integer> numbers = IntStream.of(arr) 
                                 .mapToObj(Integer::valueOf)
                                 .collect(Collectors.toList());
Assert.assertEquals(Arrays.asList(1, 2, 3, 4, 5), numbers);

2.3 Integer[] to List<Integer> using Arrays.asList loop

In this example we use a reference array or object array to convert it to List. We can directly we asList method of Arrays class to convert it to List.

Integer[] arr = { 1, 2, 3, 4, 5 };
List<Integer> numbers = Arrays.asList(arr);

2.4 Integer[] to List<Integer> using Arrays.stream

To convert the object array to List we use Arrays.stream method.

Integer[] arr = { 1, 2, 3, 4, 5 };
List<Integer> numbers = Arrays.stream(arr).collect(Collectors.toList());

3. Conclusion

In this article, we saw few different ways to convert array to List. This article determines how to establish a bridge between array and Collection.