code: public GitCheckoutResponse checkout(File repositoryPath, GitCheckoutOptions options, Ref branch,
                                          File path) throws JavaGitException, IOException {
          CheckUtilities.checkFileValidity(repositoryPath);
          GitCheckoutParser parser = new GitCheckoutParser();
          List<File> paths = new ArrayList<File>();
          paths.add(path);
          List<String> command = buildCommand(options, branch, paths);
          GitCheckoutResponse response = (GitCheckoutResponse) ProcessUtilities.runCommand(repositoryPath,
                  command, parser);
          return response;
      }
docs: Checks out a file from repository from a particular branch