docs: private String replaceExtName(final String aFileName){
          final int index = aFileName.indexOf(SHARP);
          if (aFileName.startsWith(SHARP)){
              return aFileName;
          } else if (index != -1){
              final String fileName = aFileName.substring(0, index);
              final int fileExtIndex = fileName.lastIndexOf(DOT);
              return (fileExtIndex != -1)
                      ? fileName.substring(0, fileExtIndex) + targetExt + aFileName.substring(index)
                              : aFileName;
          } else {
              final int fileExtIndex = aFileName.lastIndexOf(DOT);
              return (fileExtIndex != -1)
                      ? (aFileName.substring(0, fileExtIndex) + targetExt)
                              : aFileName;
          }
      }