java - Insert Space After Capital letter

Question

How to covert "HelloWorld" to "Hello World".The splitting has to take place based on The Upper-Case letters ,but should exclude the first letter.

P.S:I'm aware of using String.split and then combining.Just wanted to know if there is a better way.

Answer 1

String output = input.replaceAll("(\p{Ll})(\p{Lu})","$1 $2");

This regex searches for a lowercase letter follwed by an uppercase letter and replaces them with the former, a space and the latter (effectively separating them with a space). It puts each of them in a capturing group () in order to be able to re-use the values in the replacement string via back references ($1 and $2).

To find upper- and lowercase letters it uses p{Ll} and p{Lu} (instead of [a-z] and [A-Z]), because it handles all upper- and lowercase letters in the Unicode standard and not just the ones in the ASCII range (this nice explanation of Unicode in regexes mostly applies to Java as well).