code: private void addFiles(FileSet fs) {
  
          // Get the files included in the fileset.
          DirectoryScanner ds = fs.getDirectoryScanner(getProject());
  
          // The base directory for all files.
          File basedir = ds.getBasedir();
  
          // Loop over each file creating a File object.
          for (String f : ds.getIncludedFiles()) {
              if (SourceType.hasSourceFileExtension(f)) {
                  sourceFiles.add(new File(basedir, f));
              }
          }
      }
docs: Utility method that adds all of the files in a fileset to the list of
  files to be processed. Duplicate files appear only once in the final
  list. Files not ending with a valid source file extension are ignored.
  
  @param fs
  FileSet from which to get the file names