How to use the string returned by one class in another class

What I have is a class (Rev) which is able to convert string into another string. I have tried to use the output (converted) string in another class. Making the output string public does not work on my hands. I am also not able to recall the method from Rev class. I would like to avoid exporting the output string into the file and importing it once again for another conversion, because I am sure that there is much more fancy way to do this. As you can see I am pretty new in java. Any help appreciated 🙂 The code looks like this:

public class Rev {     public static void main (String[] args){         String s = "ACGTACCCC";         char[] reverse = new char[s.length()];         for (int i = 0; i < reverse.length; i++) {             switch (s.charAt(i)) {                 case 'A':                     reverse[i] = 'T';                     break;                 case 'T':                     reverse[i] = 'A';                     break;                 case 'C':                     reverse[i] = 'G';                     break;                 case 'G':                     reverse[i] = 'C';                     break;                 default: //handle error when invalid char             }         }         s = new String(reverse);         System.out.println(s);     } }