Extract overlapping matches using split

Question

How can I extract overlapping matches from an input using String.split()?

For example, if trying to find matches to "aba":

String input = "abababa";
String[] parts = input.split(???);

Expected output:

[aba, aba, aba]

Answer 1

String#split will not give you overlapping matches. Because a particular part of the string, will only be included in a unique index, of the array obtained, and not in two indices.

You should use Pattern and Matcher classes here. You can use this regex: -

Pattern pattern = Pattern.compile("(?=(aba))");

And use Matcher#find method to get all the overlapping matches, and print group(1) for it.

The above regex matches every empty string, that is followed by aba, then just print the 1st captured group. Now since look-ahead is zero-width assertion, so it will not consume the string that is matched. And hence you will get all the overlapping matches.

String input = "abababa";
String patternToFind = "aba";

Pattern pattern = Pattern.compile("(?=" + patternToFind + ")");
Matcher matcher = pattern.matcher(input);

while (matcher.find()) {
    System.out.println(patternToFind + " found at index: " + matcher.start());
}

Output: -

aba found at index: 0
aba found at index: 2
aba found at index: 4

Answer 2

I would use indexOf.

for(int i = text.indexOf(find); i >= 0; i = text.indexOf(find, i + 1))
   System.out.println(find + " found at " + i);