public class HasXExample {
    public static boolean hasX(String s) {
        /* Now that you know the base case(s), figure out 
         * what the answer for the base case is. */
        if (s.equals("")) {
            return false;
        }
            /* Now, we have to figure out the recursive step. 
             * First, write down what the function we are writing does. */
            // This function...tests if a string has an 'x' in it
        else {
            /* Then, ask the question: 
             * “What is the smallest piece of the problem I can break off?” */
            // The smallest piece I can break off is...
                // one character: the first character
            char first = s.charAt(0);

            /* Figure out the answer to the question for the tiny problem.
             * and do the rest recursively. */
            return first == 'x' || hasX(s.substring(1));
        }
    }
    
    public static void main(String[] args) {
        String[] tests    = {"hello", "xylophone", "abcdx", "qrst"};
        boolean[] correct = {false,   true,        true,    false};
        
        for (int i = 0; i < tests.length; i++) {
            System.out.println("hasX(" + tests[i] + ") -> " + hasX(tests[i]) + 
                               " (should be " + correct[i] + ")");
        }
    }
}