code: static Collection<File> getCheckpointDirs(Configuration conf,
        String defaultName) {
      Collection<String> dirNames = conf.getStringCollection("fs.checkpoint.dir");
      if (dirNames.size() == 0 && defaultName != null) {
        dirNames.add(defaultName);
      }
      Collection<File> dirs = new ArrayList<File>(dirNames.size());
      for (String name : dirNames) {
        dirs.add(new File(name));
      }
      return dirs;
    }
docs: Retrieve checkpoint dirs from configuration.
  
  @param conf the Configuration
  @param defaultValue a default value for the attribute, if null
  @return a Collection of URIs representing the values in
  dfs.namenode.checkpoint.dir configuration property