Mapreduce way to convert all elements of String[] to int[] in Java?

Question

You can convert all elements of a String array to ints and store them in an int array like this:

public static final void main(String[] args) {
    String input = "1 2 5 17 23 12 5 72 123 74 13 19 32";
    String[] strAr = input.split(" ");

    int[] output = parseIntArray(strAr);
}

private static int[] parseIntArray(String[] strAr) {
    // convert to int[] one by one
    int[] output = new int[strAr.length];
    for (int i = 0; i < strAr.length; i++) {
        output[i] = Integer.parseInt(strAr[i]);
    }

    return output;
}

How can you write the parseIntArray(String[]) method in a map-reduce fashion in Java?

I heard that there is a simple way to do this with lambdas in Java 8. Was there also a map-reduce fashion way to do this prior to Java 8? I know this is two questions in one; however I believe that they are so closely related that it is better for the community to have both of these answers on one page.

Answer 1

One way to write it would be:

private static int[] parseIntArray(String[] strAr) {
  return Stream.of(strAr).mapToInt(Integer::parseInt).toArray();
}

You could also start directly from the string:

private static final Pattern splitOnSpace = Pattern.compile(" ");

private static int[] parseIntArray(String str) {
  return splitOnSpace.splitAsStream(str).mapToInt(Integer::parseInt).toArray();
}