Swapping of Two Strings withought using third variable(Temp also) in java

public class Swapstring {
        public static void main(String[] args) {
            String a = "test";
            String b = "paper";

            a = a + b;
            System.out.println(a.length());
            b = a.substring(0, a.length()  - b.length());
            System.out.println("b value is:" +b);
            System.out.println(b.length());

            a = a.substring(b.length(), a.length());

            System.out.println("a value is:" +a);
        }
}