code: public void setName(String fieldName) {
          if (m_name != null) {
              throw new IllegalArgumentException("Field name is already set: " + m_name);
          }
          if (!isValidFieldName(fieldName)) {
              throw new IllegalArgumentException("Invalid field name: " + fieldName);
          }
          m_name = fieldName;
      }
docs: Set this field's name to the given valid. An IllegalArgumentException is thrown
  if the name is already assigned or is not valid.
  
  @param fieldName New name for field.