Convert the string into stringBuilder in java

I have one method which returns the string but I want the data inside the method in StringBuilder and convert it into string then how can I do it?

  public String[][] getDataOfJD(List<JobDescriptionField> jdFields) {
  int i = 0;
  String [][] data = new String[jdFields.size()][];
  for(JobDescriptionField field : jdFields) {
      if (i > 0){
          String messages = "";
          for (String message : field.getMessages()){
             messages += message;
          }
     data [i] = new String[]{field.getTitle(), field.getField(), messages, field.getScore() + ""};
  }
    i++;
    score = score + field.getScore();
  }
  return data;
  }

From above example field.getTitle(), field.getField() are of String type And if I want the data in StringBuilder and needs to convert it into string but if I tried to do it by return data.toString then it is giving error. Please Help me.