public class Foo {

    static String a = new String("A");

    static String b = new String("B");

    public static void main(String[] args) {

        operate(a, b);

    System.out.println(a + ","+b);

}

    static void operate(String x, String y) {

                a = y + x;

                x = a + x + y;

    }

}