Java: Understanding the String replaceAll() method

Question

I\'m looking to figure out the answer to this problem here.

First off,

blah[abc] = blah[abc].replaceAll(\"(.*) (.*)\", \"$2, $1\");

Answer 1

Your regular expression "(.)(.)" will be of this sort : "(x)(y)" this will be replaced by "$2,$1.

Answer 2

(.*) - would be a pattern to match any number of characters. Parentheses would be to mark it as a sub pattern (for back reference).

$2 & $1 - are back references. These would be things matched in your second and first sub pattern.

Basically replaceAll("(.) (.)", "$2, $1") would find characters separated by a space, then add a comma before the space, in addition to flipping the parts. For example:

a b => b, a
Hello world => Hellw, oorld

Not sure about nesting... Can you post the code you're running?