I want to split the string "aaaabbbccccaaddddcfggghhhh" into "aaaa", "bbb", "cccc". "aa", "dddd", "c", "f" and so on.
I tried this:
String arr = "aaaabbbccccaaddddcfggghhhh".split("(.)(?!\\1)");
String str = "aaaabbbccccaaddddcfggghhhh"; String out = str.split("(?<=(.))(?!\\1)"); System.out.println(Arrays.toString(out)); => [aaaa, bbb, cccc, aa, dddd, c, f, ggg, hhhh]
Explanation: we want to split the string at groups of same chars, so we need to find out the "boundary" between each group. I'm using Java's syntax for positive look-behind to pick the previous char and then a negative look-ahead with a back reference to verify that the next char is not the same as the previous one. No characters were actually consumed, because only two look-around assertions were used (that is, the regular expresion is zero-width).