StringInverse.java

package Lesson3.KeyPoint5;

import java.util.Arrays;

/**
 * Created by Юрий on 12.01.2016.
 */
public class StringInverse {
    public static void main(String[] args) {

        System.out.println(inverse("Yurok"));
        System.out.println(inverse("Programmer"));
    }

    static String inverse(String str) {
        char[] arr = str.toCharArray();
        char[] tmp = new char[arr.length];
        int count = arr.length - 1;

        for (int i = 0; count >= 0; i++) {
            tmp[count] = arr[i];
            count--;
        }
        return new String(tmp);
    }
}

Как обычно забыли проверку на null.