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Is it possible to convert ArrayList<Integer> into ArrayList<Long>? [duplicate]

Posted by: admin December 28, 2021 Leave a comment


In my application I want to convert an ArrayList of Integer objects into an ArrayList of Long objects. Is it possible?


Not in a 1 liner.

List<Integer> ints = Arrays.asList(1,2,3,4,5,6,7,8,9);
int nInts = ints.size();
List<Long> longs = new ArrayList<Long>(nInts);
for (int i=0;i<nInts;++i) {

// Or you can use Lambda expression in Java 8

List<Integer> ints = Arrays.asList(1,2,3,4,5,6,7,8,9);
List<Long> longs = ints.stream()


No, you can’t because, generics are not polymorphic.I.e., ArrayList<Integer> is not a subtype of ArrayList<Long>, thus the cast will fail.
Thus, the only way is to Iterate over your List<Integer> and add it in List<Long>.

List<Long> longList = new ArrayList<Long>();
for(Integer i: intList){


ArrayList<Long> longList = new ArrayList<Long>();

Iterator<Integer> it = intList.iterator();
    Integer obj = it.next();
    longList.add(obj); //will automatically convert Int to Long