Split at every i-th and j-th char

Question

I need to split a string at every i-th and j-th character, where i and j can change according to input parameters. If for example i have an input

String s = "1234567890abcdef";
int i = 2;
int j = 3;

I want my output to be an array of:

[12, 345, 67, 890, ab, cde, f]

I found a compact regex to split at every n-th char. Example for n = 3 using "(?<=\\G...)" or "(?<=\\G.{3})"

String s = "1234567890abcdef";
int n = 3;
System.out.println(Arrays.toString(s.split("(?<=\\G.{"+n+"})")));

//output: [123, 456, 789, 0ab, cde, f]

How to modify the above regex to split at every 2nd and 3rd char alternately?

A naive chaining like "(?<=\\G.{2})(?<=\\G.{3})" did not work.

Answer 1

I don't think you can do this with split(), because every match should be aware of the pattern previously matched.

If you don't want to manually iterate over the string's characters, you can use something like this:

Matcher m = Pattern.compile("(.{0,2})(.{0,3})").matcher("1234567890abcdef");
List<String> list = new ArrayList<>();
while (m.find()) {
  for (int i = 1; i <= 2; i++) {
    if (!m.group(i).isEmpty()) {
      list.add(m.group(i));
    }
  }
}
System.out.println(list);  // prints [12, 345, 67, 890, ab, cde, f]