Conversion of int[] to Integer[], List<Integer> and vice-versa.

December 17, 2021

This has been a real pain point while solving problems involving data structures and algorithms. Here, I will collect the conversions which is easy and handy to use

NB: >= Java 8

int[] to Integer[]

int[] array = {1,2,3,4,5,6,7,8,9,10};
Integer[] boxedArray = Arrays.stream(data).boxed().toArray( Integer[]::new );

int[] to List

int[] array = {1,2,3,4,5,6,7,8,9,10};
List<Integer> boxedList = Arrays.stream(data).boxed().collect(Collectors.toList());

List to int[]

List<Integer> list = new ArrayList<>();
list.add(1);
list.add(2);
list.add(3);

int[] primitiveArray = list.stream().mapToInt(Integer::intValue).toArray();

List to Integer[]

List<Integer> list = new ArrayList<>();
list.add(1);
list.add(2);
list.add(3);

Integer[] intArray = new Integer[list.size()];
intArray = list.toArray(intArray);

References
https://stackoverflow.com/questions/880581/how-to-convert-int-to-integer-in-java\ https://stackoverflow.com/questions/960431/how-to-convert-listinteger-to-int-in-java\ https://devqa.io/convert-list-to-array-in-java/