Whats the best way to recursively reverse a string in Java?

Question

I have been messing around with recursion today. Often a programming technique that is not used enough.

I set out to recursively reverse a string. Here\'s what I cam

Answer 1

You don't want to nest too deeply. Divide-and-conquer is the way to go. Also reduces total size of temporary strings and is amenable to parallelisation.

public static String reverseString(String str) {
    int len = str.length();
    return len<=1 ? str : (
        reverseString(str.substring(len/2))+
        reverseString(str.substring(0, len/2))
    );
}

(Not tested - this is stackoverflow.)

String.concat instead of + would improve performance at the expense of clarity.

Edit: Just for fun, a tail-recursion friendly version of the naive algorithm.

public static String reverseString(String str) {
    return reverseString("", str);
}
private static String reverseString(String reversed, String forward) {
    return forward.equals("") ? reversed : (
         reverseString(reversed+forward.charAt(0), forward.substring(1)) 
    );
}

Correct handling of surrogate pairs is left to the interested reader.