除了递归遍历，还可以使用基于访问者的方法。

下面的代码是使用基于访问者的遍历方法。我们期望程序的输入是要遍历的根目录。

public interface Visitor {
    void visit(DirElement d);
    void visit(FileElement f);
}

public abstract class Element {
    protected File rootPath;
    abstract void accept(Visitor v);

    @Override
    public String toString() {
        return rootPath.getAbsolutePath();
    }
}

public class FileElement extends Element {
    FileElement(final String path) {
        rootPath = new File(path);
    }

    @Override
    void accept(final Visitor v) {
        v.visit(this);
    }
}

public class DirElement extends Element implements Iterable<Element> {
    private final List<Element> elemList;
    DirElement(final String path) {
        elemList = new ArrayList<Element>();
        rootPath = new File(path);
        for (File f : rootPath.listFiles()) {
            if (f.isDirectory()) {
                elemList.add(new DirElement(f.getAbsolutePath()));
            } else if (f.isFile()) {
                elemList.add(new FileElement(f.getAbsolutePath()));
            }
        }
    }

    @Override
    void accept(final Visitor v) {
        v.visit(this);
    }

    public Iterator<Element> iterator() {
        return elemList.iterator();
    }
}

public class ElementWalker {
    private final String rootDir;
    ElementWalker(final String dir) {
        rootDir = dir;
    }

    private void traverse() {
        Element d = new DirElement(rootDir);
        d.accept(new Walker());
    }

    public static void main(final String[] args) {
        ElementWalker t = new ElementWalker("C:\\temp");
        t.traverse();
    }

    private class Walker implements Visitor {
        public void visit(final DirElement d) {
            System.out.println(d);
            for(Element e:d) {
                e.accept(this);
            }
        }

        public void visit(final FileElement f) {
            System.out.println(f);
        }
    }
}

在Java 7中，你可以使用以下类:

import java.io.IOException;
import java.nio.file.FileVisitResult;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.SimpleFileVisitor;
import java.nio.file.attribute.BasicFileAttributes;

public class MyFileIterator extends SimpleFileVisitor<Path>
{
    public MyFileIterator(String path) throws Exception
    {
        Files.walkFileTree(Paths.get(path), this);
    }

    @Override
    public FileVisitResult visitFile(Path file,
            BasicFileAttributes attributes) throws IOException
    {
        System.out.println("File: " + file);
        return FileVisitResult.CONTINUE;
    }

    @Override
    public FileVisitResult preVisitDirectory(Path dir,
            BasicFileAttributes attributes) throws IOException
    {
        System.out.println("Dir: " + dir);
        return FileVisitResult.CONTINUE;
    }
}

这段代码可以运行了

public static void main(String... args) {
    File[] files = new File("D:/").listFiles();
    if (files != null) 
       getFiles(files);
}

public static void getFiles(File[] files) {
    for (File file : files) {
        if (file.isDirectory()) {
            getFiles(file.listFiles());
        } else {
            System.out.println("File: " + file);
        }
    }
}

除了递归遍历，还可以使用基于访问者的方法。

下面的代码是使用基于访问者的遍历方法。我们期望程序的输入是要遍历的根目录。

public interface Visitor {
    void visit(DirElement d);
    void visit(FileElement f);
}

public abstract class Element {
    protected File rootPath;
    abstract void accept(Visitor v);

    @Override
    public String toString() {
        return rootPath.getAbsolutePath();
    }
}

public class FileElement extends Element {
    FileElement(final String path) {
        rootPath = new File(path);
    }

    @Override
    void accept(final Visitor v) {
        v.visit(this);
    }
}

public class DirElement extends Element implements Iterable<Element> {
    private final List<Element> elemList;
    DirElement(final String path) {
        elemList = new ArrayList<Element>();
        rootPath = new File(path);
        for (File f : rootPath.listFiles()) {
            if (f.isDirectory()) {
                elemList.add(new DirElement(f.getAbsolutePath()));
            } else if (f.isFile()) {
                elemList.add(new FileElement(f.getAbsolutePath()));
            }
        }
    }

    @Override
    void accept(final Visitor v) {
        v.visit(this);
    }

    public Iterator<Element> iterator() {
        return elemList.iterator();
    }
}

public class ElementWalker {
    private final String rootDir;
    ElementWalker(final String dir) {
        rootDir = dir;
    }

    private void traverse() {
        Element d = new DirElement(rootDir);
        d.accept(new Walker());
    }

    public static void main(final String[] args) {
        ElementWalker t = new ElementWalker("C:\\temp");
        t.traverse();
    }

    private class Walker implements Visitor {
        public void visit(final DirElement d) {
            System.out.println(d);
            for(Element e:d) {
                e.accept(this);
            }
        }

        public void visit(final FileElement f) {
            System.out.println(f);
        }
    }
}

import java.io.File;

public class Main {
    public static void main(String[] args) {
        loopFiles(new File("C:\\Users\\serge.klimkovitch\\Documents"));
    }

    private static void loopFiles(File element) {
        if (element.isDirectory()) {
            for (File currentFile : element.listFiles()) {
                loopFiles(currentFile);
                System.out.println(currentFile);
            }
        }
    }
}

根据@Michael的回答，添加检查listFiles是否返回null

static Stream<File> files(File file) {
    return file.isDirectory()
            ? Optional.ofNullable(file.listFiles()).map(Stream::of).orElseGet(Stream::empty).flatMap(MainActivity::files)
            : Stream.of(file);
}

或者使用light - weight- stream - api，支持Android5和Android6

static Stream<File> files(File f) {
    return f.isDirectory() ? Stream.ofNullable(f.listFiles()).flatMap(MainActivity::files) : Stream.of(f);
}