Why is NIO.2 FileVisitor type generic?

Question

I'm doing some research on Java NIO.2 and its file operations, and currently I'm playing with filetree-walking functions and classes.

NIO.2 FileVisitor API is wonderful, it's a shame that such thing has been added to Java SE only recently, not ten years ago. However, there is something which slightly bothers me: what is the point of making FileVisitor interface generic?

Every single example on the net shows how to use it with Files.walkFileTree() which implies that we are using FileVisitor<Path> type. But I just cannot see any use for this interface for things other than Path. Well, it may be possible to use FileVisitor to walk other kinds of trees (in-memory ones?), but this just doesn't feel right: this interface and related classes have very specific names semantically tied to files, and also FileVisitor's methods throw IOExceptions.

So, were there any reasons for parameterizing FileVisitor type?

Answer 1

With generics the same interface can be used for other types of paths. As shown in the following (simplified) code fragment, the interface works nice with java.io.File:

FileVisitResult walk(File file, FileVisitor<File> visitor)
    throws IOException
{
    if (file.isDirectory()) {
        visitor.preVisitDirectory(file, null);
        for (File child : file.listFiles()) {
            walk(child, visitor);
        }
        return visitor.postVisitDirectory(file, null);
    } else {
        return visitor.visitFile(file, null);
    }
}

Answer 2

Do you use GitHub? This would be a perfect opportunity to use the FileVisitor to implement an API to GitHub that allows you to explore/visualise GitHub projects. For that matter almost any SCC system could make use of a different class as the file locator

And how about using a FileVisitor<ZipEntry> for traversing zip files.

If an API is potentially usable with multiple objects as its target it just makes sense to make it generic. I think not making it generic would be the mistake that should be considered foolish.