Method that replaces a specified String by another one in all of the first String's extension. In this case, all instances of the letter "T" in the input string are replaced by "U"

Bio.java

import java.lang.StringBuilder;

public class Bio {
    
    public static String dnaToRna(String dna){
        StringBuilder strb = new StringBuilder(dna);
        
        while(strb.indexOf("T") != -1) {
          strb.replace(strb.indexOf("T"),strb.indexOf("T")+1,"U");
        }

        String rna = strb.toString();
        return rna;
    } 
}