为什么列表保持不变？

Question

我尝试创建一个小应用程序，它使用文件遍历器递归地读取文件系统中指定位置的内容。我有这样的代码：

/* Imports here */

public class App {

    private static Scanner inp;
    public static List<Node> Tree = new ArrayList<Node>();

    public static void main(String[] args) {
        String FFiles;

        System.out.print("Enter root directory: ");
        inp = new Scanner(System.in);

        FileSystem fileSystem = FileSystems.getDefault();
        Path rootPath = fileSystem.getPath(inp.nextLine());

        FileVisitor<Path> simpleFileVisitor = new SimpleFileVisitor<Path>() {
              public Path VisitedDirectory = rootPath;
              public List<Node> files = new ArrayList<Node>();


              @Override
              public FileVisitResult preVisitDirectory(Path dir,BasicFileAttributes attrs) throws IOException {
                if (dir != VisitedDirectory) {
                    Node directory = new Node(dir.getFileName().toString(), "directory", files, dir.toString());
                    files.add(directory);
                    Node VisDirectory = new Node(VisitedDirectory.getFileName().toString(), "directory", files, dir.toString());
                    Tree.add(VisDirectory);

                    files.clear();
                }
                return FileVisitResult.CONTINUE;
              }

              @Override
              public FileVisitResult visitFile(Path visitedFile,BasicFileAttributes fileAttributes) throws IOException {
                Node file = new Node(visitedFile.getFileName().toString(), "file", null, visitedFile.toString());
                files.add(file);
                return FileVisitResult.CONTINUE;
              }
        };



        try {
            Files.walkFileTree(rootPath, simpleFileVisitor);
        } catch (IOException ioe) {
            ioe.printStackTrace();
        }

        for (Node n : Tree) {
            System.out.println(n);
        }
    }

这里有一个问题:为什么它只读取(显示)目录？P.S Node类只是几个变量，声明如下：

public class Node {
    @Override
    public String toString() {
        return "Node [path=" + path + "]";
    }

    public String name;
    public String path;
    public  String type;
    public List<Node> children = new ArrayList<Node>();
    public Node(String name, String type, List<Node> children, String path) {
        this.name = name;
        this.type = type;
        this.children = children;
        this.path = path;
    }
}

Answer 1

你把files列表弄得乱七八糟。您只能创建单个实例。因此，您的new Node(VisitedDirectory.getFileName().toString(), "directory", files, dir.toString())实际上并不复制文件列表，而只是存储一个引用。您的files.clear()调用将清除您拥有的所有文件列表。这就是为什么只有您添加到Tree中的节点才能存活。

请将Tree重命名为小写。这样，人们就会认为Tree.add()调用了Tree类上的静态方法。