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From: Robert Klemme <shortcutter@googlemail.com>
Newsgroups: comp.lang.java.programmer
Subject: Re: The first 10 files
Date: Mon, 25 Feb 2013 21:53:56 +0100
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On 24.02.2013 23:50, Arne Vajh=F8j wrote:
> On 1/27/2013 7:55 AM, Robert Klemme wrote:
>> On 27.01.2013 03:43, Arne Vajh=F8j wrote:
>>> On 1/26/2013 9:35 PM, Arne Vajh=F8j wrote:
>>>> On 1/26/2013 9:02 PM, Arved Sandstrom wrote:
>>
>>>> If OP happens to be on Java 7, then I will suggest using:
>>>>
>>>> java.nio.file.Files.newDirectoryStream(dir)
>>>>
>>>> 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.io.IOException;
>>> 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 =3D
>>> Files.newDirectoryStream(Paths.get("/work")).iterator();
>>>          int n =3D 0;
>>>          while(dir.hasNext() && n < 10) {
>>>              System.out.println(dir.next());
>>>          }
>>>      }
>>> }
>>
>> For earlier Java versions we could emulate that with a second thread.
>>
>> package file;
>>
>> import java.io.File;
>> import java.io.FileFilter;
>> 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 =3D new ArrayList<File>();
>>
>>      public CountFilterThread(File dir, int maxFiles,
>> BlockingQueue<List<File>> queue) {
>>        this.dir =3D dir;
>>        this.maxFiles =3D maxFiles;
>>        this.queue =3D queue;
>>      }
>>
>>      @Override
>>      public void run() {
>>        try {
>>          dir.listFiles(this);
>>
>>          if (filesSeen !=3D null) {
>>            send();
>>          }
>>        } catch (InterruptedException e) {
>>          e.printStackTrace();
>>        }
>>      }
>>
>>      private void send() throws InterruptedException {
>>        queue.put(filesSeen);
>>        filesSeen =3D null;
>>      }
>>
>>      @Override
>>      public boolean accept(final File f) {
>>        try {
>>          if (filesSeen !=3D null) {
>>            filesSeen.add(f);
>>
>>            if (filesSeen.size() =3D=3D maxFiles) {
>>              send();
>>              assert filesSeen =3D=3D null;
>>            }
>>          }
>>
>>          return false;
>>        } catch (InterruptedException e) {
>>          throw new IllegalStateException(e);
>>        }
>>      }
>>    }
>>
>>    private static final int[] LIMITS =3D { 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 =3D new File(s);
>>
>>        if (dir.isDirectory()) {
>>          for (final int limit : LIMITS) {
>>            final SynchronousQueue<List<File>> queue =3D new
>> SynchronousQueue<List<File>>();
>>            final CountFilterThread cf =3D new CountFilterThread(dir,
>> limit, queue);
>>            cf.setDaemon(true);
>>            final long t1 =3D System.nanoTime();
>>            cf.start();
>>            final List<File> entries =3D queue.take();
>>            final long delta =3D System.nanoTime() - t1;
>>            System.out.printf("It took %20dus to retrieve %20d files,
>> %20.5fus/file.\n",
>>                TimeUnit.NANOSECONDS.toMicros(delta), entries.size(),
>> (double) TimeUnit.NANOSECONDS.toMicros(delta)
>>                    / entries.size());
>>          }
>>        } else {
>>          System.out.println("Not a directory.");
>>        }
>>      }
>>
>>      System.out.println("done");
>>    }
>>
>> }
>>
>> https://gist.github.com/4648256
>>
>> 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?

No.

	robert



--=20
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/