Incrementing every letter in a string that occupies an odd position.

Question

Hi, for an "encryption" project, i need your help creating a method that will be incrementing by 5 every char in a string that occupies an odd position in that same string.
For example : 'adam' should return 'aiar'
-Method can't use arrays.
-Method can't use regular expressions like 'split' etc..in order words the teacher wants us to use the simplest stuff inside the String class.
-Only letters must be modified.
so far i have this : (names of values are in french, sorry)
public class Main {
public static String incrementerDeCinqImpaires (String chaine) {
char j = chaine.charAt(1);
char x = chaine.charAt(3);
char o = chaine.charAt(5);
j+=5;
x+=5;
o+=5;
System.out.println(x);
System.out.println(j);
System.out.println(o);
String   tmpString = chaine.replace( chaine.charAt(1), j );
String   tmpString2 = tmpString.replace( tmpString.charAt(3), x );
String   tmpString3 = tmpString2.replace( tmpString2.charAt(5), o );
System.out.println( "Original = " + chaine );
System.out.println( "Result   = " + tmpString3 );
return tmpString3;
public static void main (String args [] ) {
       System.out.println (incrementerDeCinqImpaires("adam"));
}The thing is i need a "for" loop (which has been a nightmare for me trying to figure out how to make it) in order to increment every odd positioned char in the string.
So all I need really is to sum up what i posted above inside a for loop (or more). Then just add ifs and elses so i can increment only letters.

Answer 1

I don't think String.replace will do what you want. What happens when a single letter appears in an even-numbered position and then in a later odd-numbered position?
Can you use StringBuilder?
Or you can do a bunch of String appends (i.e., use StringBuilder implicitly), one character at a time, in a loop.
By the way you haven't done the part where you check that the character is a letter.
Also, what do you do with the last five letters of the alphabet? (Regardless of the alphabet you're using.) You could end up inserting control characters or characters that you can't print in your locale. Do you wrap?