Regex to remove spaces between numbers only

Question

I need to remove the spaces between numbers only, so that a string like this:

"Hello 111 222 333 World!"

becomes

"Hello 111222333 World!"

I've tried this:

message = message.replaceAll("[\\d+](\\s+)[\\d+]", "");

Doesn't seem to get it done.

Answer 1

How about:

message = "Hello 111 222 333 World!".replaceAll("(\\d)\\s(\\d)", "$1$2");

Gives:

"Hello 111222333 World!"

Answer 2

You can use this lookaround based regex:

 String repl = "Hello 111 222 333 World!".replaceAll("(?<=\\d) +(?=\\d)", "");
 //=> Hello 111222333 World!

This regex "(?<=\\d) +(?=\\d)" makes sure to match space that are preceded and followed by a digit.