C variable format to Java Variable String format : snakeCase to java convention and vice versa

How to convert snake case format containing underscore to java variable format and vice versa?
 Usually c variable contains underscore between words but java contains firstletter is lowercase and other first letter in upper case.

This is very famous test program usually asked in online test.



example :
 input = bb_cann_fb_hnh
output = bbCannFbHnh

and vice versa.

public class VariableFormatter {
public static void main( String[] args )
    {
        System.out.println(modifyVariableString("bb_cann_fb_hnh"));
        System.out.println(modifyVariableString("bbCannFb"));
     
    }
 
 
   private static String modifyVariableString(String s) {

   String output;

//check if it is c variable

   if(s.contains("_")){
   output= javaFormatter(s);
   }else{
   output= cFormatter(s);
   }
return output;
}


private static String cFormatter(String string) {
   string= string.replaceAll("([A-Z])", "_$1").toLowerCase();
return string;
}


static String javaFormatter(String s){
  String[] elements= s.split("_");

  StringBuilder sb = new StringBuilder(elements[0]);
    for(int i=1;i<elements.length;i++){
    elements[i]=elements[i].substring(0, 1).toUpperCase()+elements[i].substring(1);
    sb.append(elements[i]);
    }
   
    String output=sb.toString();
   
    return output;
    }
}