Is it possible to convert an Arraylist<Double> to Arraylist<Integer>?

Question

So, guys, I’d like to know if there is and how to make the conversion of a ArrayList<Double> in a ArrayList<Integer>?

Answer 1

You need to do something so that all items from the original list return its integer value. This can be done with the method intValue().

Note that obviously the decimal part of the numbers will be lost.

Using Java 8

List<Double> doubles = /* lista original */;

List<Integer> integers = doubles.stream() 
                                .map(d -> d.intValue())
                                .collect(Collectors.toList());

^{See working on Repl.it.}

In previous versions.

Note that the right-hand type inference of the generic declaration was only inserted in Java 7 - see documentation. Still, the answer is valid for all lower versions, just need to change the instantiation of Arraylist of new ArrayList<>() for new ArrayList<Integer>().

List<Double> doubles = /* lista original */;

List<Integer> integers = new ArrayList<>();

for(Double d : doubles) {
    integers.add(d.intValue());
}

^{See working on Repl.it.}