Printing reverse of any String without using any predefined function?

Question

How to print the reverse of the String java is object orientated language without using any predefined function like reverse()?

Answer 1

I had this a while back, and having answered with the obvious StringBuffer.reverse() answer, they then asked 'Can you reverse a char array without using those API methods and achieve the result without spooling into a new char array?'

At the time I recognised that I only needed to iterate over half the length of the char array, but made a bit of a hash of explaining the actual code that needed to go into it (it was a verbal question). Anyway, I tried it when I got home and came up with this:

public class StringReverse {

public static void main(String[] args){

    String a = "String";

    char[] aChar = a.toCharArray();

    for (int i = (aChar.length-1)/2 ; i >= 0 ; i--){
        int posA = i;
        int posB = (aChar.length-1-i);
        char tmpA = aChar[posA];
        char tmpB = aChar[posB];
        System.out.println("Setting " + posA + " to " + tmpB);
        System.out.println("Setting " + posB + " to " + tmpA);

        aChar[posA] = tmpB;
        aChar[posB] = tmpA;
    }

    System.out.println(aChar);
}

}

You can obviously achieve this with less code, but I think the temporary assignments in the method make it more clear what the code is doing.

Outputs something like:

Setting 2 to i
Setting 3 to r
Setting 1 to n
Setting 4 to t
Setting 0 to g
Setting 5 to S

gnirtS

More of an interview question than a homework question, I'd say.