How to compare all file names from a given directory java?

Question

I want to compare all file names from a given directory

Input/Output code:

static Scanner sc = new Scanner(System.in);
static String Directory = sc.next(); 
static File folder = new File(Directory);
static File[]listofFiles = folder.listFiles();
static String[] underFiles = folder.list();

public static void main(String[] args) throws IOException {
    Main main = new Main();
    main.walk(Directory);
}

public void walk( String path ) {
    File root = new File( path );
    File[] list = root.listFiles();
    if (list == null) {
        return;
    }
    for (File f : list) {
        if ( f.isDirectory() ) {
            walk( f.getAbsolutePath() );
            System.out.println( "Dir:" + f.getAbsoluteFile() );
        }
        else {
            System.out.println( "File:" + f.getName() );
        }
    }
}

The input is to give a directory path. The output will show all of the files in the given directory. How can I compare equal file names in this directory?

Answer 1

Try this:

public static void main(String[] args) throws IOException {
    String path = "/your/file-path/here";

    try (Stream<Path> paths = Files.walk(Paths.get(path))) {
        Map<String, List<Path>> map = 
                 paths.filter(Files::isRegularFile)
                      .collect(groupingBy(p -> p.getFileName().toString()));

        System.out.println(map);
    }
}

Files.walk will walk all the hierarchy of files for you. The only thing you need to do is to consume the Path s from Stream .

---

If you still want to stick with your own code. Then you might do this instead:

public static void walk(String path, Map<String, List<String>> map) {

    File root = new File(path);
    File[] list = root.listFiles();

    if (list == null) return;

    for (File f : list) {
        if (f.isDirectory()) {
            walk(f.getAbsolutePath(), map);
            System.out.println("Dir:" + f.getAbsoluteFile());
        } else {
            map.computeIfAbsent(f.getName(), k -> new ArrayList())
                    .add(f.getAbsolutePath());
            System.out.println("File:" + f.getName());
        }
    }
}

and then:

public static void main(String[] args) {
    String fileName = "/your/file-path/here";

    Map<String, List<String>> map = new HashMap<>();
    walk(fileName, map);

    System.out.println(map);
}

Answer 2

As I understand it, you want to locate directories that contain files with the same file name. For example, on a Windows machine, you may have several folders that contain image files. Usually each one of those folders will have a file named Thumbs.db . So you would like to know the names of the folders that contain a file named Thumbs.db .

The following code calls method walk of class java.nio.file.Files and manipulates the Stream returned by that method to create a Map where the Map key is the file name and the Map value is a List of all the folders that contain a file with that name.

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class WalkTree {

    public static void main(String[] args) {
        Path path = Paths.get(args[0]);
        try (Stream<Path> paths = Files.walk(path)) {
            Map<Path, List<Path>> map = paths.filter(p -> Files.isRegularFile(p))
                                             .collect(Collectors.toMap(p -> p.getFileName(),
                                                                       p -> new ArrayList<Path>(List.of(p.getParent())),
                                                                       (l1, l2) -> {l1.addAll(l2); return l1;}));
        }
        catch (IOException xIo) {
            xIo.printStackTrace();
        }
    }
}

The first parameter to the toMap method, in the above code, is a Function that returns the Map key. The second parameter is another Function that returns the Map value. And the third parameter is a BinaryOperator that merges two different Map values that both have the same Map key.