[hardwired]

Code:

import java.io.*;
import java.util.*;

public class SearchTest {
    static Random seed = new Random();
    static String[] fileNames;
    static String target;
    static long start;

    public static void main(String[] args) {
        String searchDir = ".";
        File folder = new File(searchDir);
        List<String> list = new ArrayList<String>();
        collectFileNames(folder, list);
        fileNames = list.toArray(new String[list.size()]);
        int index = seed.nextInt(fileNames.length);
        target = fileNames[index];
        System.out.printf("target = %s at index = %d of %d files%n",
                           target, index, fileNames.length);
        start = System.currentTimeMillis();
        new Thread(forward).start();
        new Thread(reverse).start();
    }

    private static void collectFileNames(File folder, List<String> list) {
        folder.setReadOnly();
        File[] files = folder.listFiles();
        for(int j = 0; j < files.length; j++) {
            list.add(files[j].getName());
            if(files[j].isDirectory())
                collectFileNames(files[j], list);
        }
    }

    private static synchronized void post(int index, long end, String caller) {
        long time = end - start;
        System.out.printf("%s found %s at index %d in %d millis%n",
                            caller, target, index, time);
    }

    private static Runnable forward = new Runnable() {
        public void run() {
            for(int j = 0; j < fileNames.length; j++) {
                if(fileNames[j].equals(target)) {
                    long end = System.currentTimeMillis();
                    post(j, end, "forward");
                    break;
                }
            }
        }
    };

    private static Runnable reverse = new Runnable() {
        public void run() {
            for(int j = fileNames.length-1; j >= 0; j--) {
                if(fileNames[j].equals(target)) {
                    long end = System.currentTimeMillis();
                    post(j, end, "reverse");
                    break;
                }
            }
        }
    };
}