code: public static boolean setCurrentFile(File databaseDir, long descriptorNumber)
              throws IOException
      {
          String manifest = descriptorFileName(descriptorNumber);
          String temp = tempFileName(descriptorNumber);
  
          File tempFile = new File(databaseDir, temp);
          writeStringToFileSync(manifest + "\n", tempFile);
  
          File to = new File(databaseDir, currentFileName());
          boolean ok = tempFile.renameTo(to);
          if (!ok) {
              tempFile.delete();
              writeStringToFileSync(manifest + "\n", to);
          }
          return ok;
      }
docs: Make the CURRENT file point to the descriptor file with the
  specified number.
  
  @return true if successful; false otherwise