Filesystem iterator, implemented with a stack instead of recursion. Returns only files.

Paths.java

import java.io.File;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Iterator;
import java.util.List;
import java.util.NoSuchElementException;

public class Paths implements Iterable<File> {

  private final File root;
  private boolean returnFiles = true;
  private boolean returnDirs = false;

  public static Paths walk(File root) {
    return new Paths(root);
  }

  public Paths(File root) {
    this.root = root;
  }

  public Paths returnDirs(boolean value) {
    this.returnDirs = value;
    return this;
  }

  public Paths returnFiles(boolean value) {
    this.returnFiles = value;
    return this;
  }

  @Override
  public Iterator<File> iterator() {
    return new Iterator<File>() {
      final List<Iterator<File>> dirStack = new ArrayList<Iterator<File>>();
      Iterator<File> currentDir = Arrays.asList(root.listFiles()).iterator();
      final boolean returnDirs = Paths.this.returnDirs;
      final boolean returnFiles = Paths.this.returnFiles;

      @Override
      public boolean hasNext() {
        return currentDir.hasNext();
      }

      @Override
      public File next() {
        while (currentDir.hasNext()) {
          final File entry = currentDir.next();
          if (entry.isDirectory()) {
            final File[] entries = entry.listFiles();
            if (entries.length > 0) {
              dirStack.add(currentDir);
              currentDir = Arrays.asList(entry.listFiles()).iterator();
              if (returnDirs) {
                return entry;
              }
            }
          } else {
            while (!currentDir.hasNext() && !dirStack.isEmpty()) {
              currentDir = dirStack.remove(dirStack.size() - 1);
            }
            if (returnFiles) {
              return entry;
            }
          }
        }
        throw new NoSuchElementException();
      }

      @Override
      public void remove() {
        throw new UnsupportedOperationException();
      }
    };
  }
}