Java' String replaceAll to replace overflow at front of string, not end.

Paul Sender :

I want to take in a string with dashes. Within the dashes there are groups of characters. That number of characters is specified by an integer K. I'm taking the dashes out to start so I have a clean String then I am using

replaceAll("(.{" + K + "})", "$0-")

To insert a - every K characters. I want the "overflow" (the left over characters after all previous characters were grouped to be put at the front of the string not the end).

For example I have a string with 8 characters:

String s = "1-23456-78";
String newS = s.replace("-", "");

newS is now 12345678

int K = 3; 
String newNewS = newS.replaceAll("(.{" + K + "})", "$0-").trim();

newNewS is 123-456-78

I want it to be 12-345-678. Anyway to reverse the replaceAll method or is there another way to do this?

sp00m :

You could play with a lookahead (demo):

.{3}(?=(?:.{3})*$)

Replace with:

-$0

In your case:

"12345678".replaceAll(".{" + K + "}(?=(?:.{" + K + "})*$)", "-$0")