java - 如何收集递归方法的结果

Question

我遍历树结构以收集叶节点的路径。您更喜欢哪种方式收集操作结果:

a) 合并 child 的结果并返回

private Collection<String> extractPaths(final Element element, final IPath parentPath) {
    final IPath path = parentPath.append(element.getLabel());
    final Collection<Element> children = getElementChildren(element);
    if (children.isEmpty())
        return Collections.singletonList(path.toString());

    final Set<String> result = new TreeSet<String>();
    for (final Element child : children)
        result.addAll(extractPaths(child, path));
    return result;
}

b) 提供结果集合作为参数并在每个递归步骤中添加新元素

private void extractPaths(final Element element, final IPath parentPath, final Set<String> result) {
    final IPath path = parentPath.append(element.getLabel());
    final Collection<Element> children = getElementChildren(element);
    if (children.isEmpty())
        result.add(path.toString());

    for (final Element child : children)
       extractPaths(child, path, result);
}

Answer 1

两者都可以毫无问题地使用。虽然，以前的解决方案更干净，因为它不会更改输入参数。没有副作用是函数式编程的本质。