public static String r(String text, int lastNdx){
        if(lastNdx < 0){
            return "";
        }else{
            return text.substring(lastNdx, lastNdx+1) + r(text, lastNdx-1);
        }
    }//end method r
    
        

String reversed = r("abcd", 3);

0	1	2	3
a	b	c	d

Call:	Stack Statement Returns:	Result:
r(text, -1) →	""	""
r(text, 0) →	a + r(text, -1)	a + "" = a
r(text, 1) →	b + r(text, 0)	b + a = ba
r(text, 2) →	c + r(text, 1)	c + ba = cba
r(text, 3) →	d + r(text, 2)	d + cba = dcba