Question

For a program I’m trying to create a directory tree. So the first part of my program uses Paths to traverse the directory I need:

public static void main(String[] args) throws IOException {
    Path startingDir = Paths.get("/home/somedirectory");
    PrintFiles pf = new PrintFiles();
    Files.walkFileTree(startingDir, pf);

}

And the PrintFiles program (I directly copied this from the guide on how to use paths for walking a tree) http://download.oracle.com/javase/tutorial/essential/io/walk.html:

public static class PrintFiles extends SimpleFileVisitor<Path> {

    //Print information about each type of file.
    @Override
    public FileVisitResult visitFile(Path file, BasicFileAttributes attr) {
        if (attr.isSymbolicLink()) {
            System.out.format("Symbolic link: %s ", file);
        } else if (attr.isRegularFile()) {
            System.out.format("Regular file: %s ", file);
        } else {
            System.out.format("Other: %s ", file);
        }
        System.out.println("(" + attr.size() + "bytes)");
        return CONTINUE;
    }

 //Print each directory visited.
    @Override
    public FileVisitResult postVisitDirectory(Path dir, IOException exc) {
        System.out.format("Directory: %s%n", dir);
        return CONTINUE;
    }

    public FileVisitResult visitFileFailed(Path file, IOException exc) {
        System.err.println(exc);
        return CONTINUE;
    }

}

I also have a generic tree program that creates a tree with any number of nodes, with the typical add nodes remove nodes etc functions (I’m not going to post the code because its long and I don’t think its really necessary since its a pretty standard implementation).

My question is how exactly do I do something where I can create a generic tree that represents the directory tree for my specific directory? I’m not exactly familiar with how the Path and File libraries work.

Thanks,
Kevin

Answer 1

You’ll need to implement preVisitDirectory, postVisitDirectory and visitFile. And you’ll need to hold the “current node” in your visit implementation.

• In pre create a new node, add it to currentNode and then set currentNode = newNode
• In visitFile create a new leaf node and add it to currentNode
• In post set currentNode = currentNode.getParent()

So sort of like a stack operation where you “push” in preVisit and “pop” in postVisit.