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Re: slow as molasses

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In article 
<e160619b-d172-4986-8e05-880d27473c5f@k15g2000yqd.googlegroups.com>,
 bob <bob@coolgroups.com> wrote:

> So, I wrote some code, but it is slow as molasses.  Any easy ways to
> speed this up?
[...]
> 			Scanner s = new Scanner(is);
[...]

After measuring, buffering and considering double, helpfully
suggested in adjacent answers, StreamTokenizer [1] may prove
measurably faster than Scanner [2]. One caveat: StreamTokenizer
can't parse scientific notation. Workaround's are possible [3,4],
although I haven't tested any.

Focusing on just the parsing, the example below produces the
following results:

Token: 5165000
Scan:  681903000
Token: 427000
Scan:  185379000
Token: 878000
Scan:  63467000
Token: 398000
Scan:  63480000
Token: 570000
Scan:  62084000

import java.io.IOException;
import java.io.StreamTokenizer;
import java.io.StringReader;
import java.util.Random;
import java.util.Scanner;

public class ScannerTest {

    private static final Random r = new Random();
    private static final int N = 10000;

    public static void main(String[] args) {
        StringBuilder sb = new StringBuilder(N);
        for (int i = 0; i < N; i++) {
            sb.append(r.nextGaussian());
            sb.append('\n');
        }
        String s = sb.toString();
        for (int i = 0; i < 5; i++) {
            long start = System.nanoTime();
            tokenize(s);
            System.out.println("Token: " + (System.nanoTime() - start));
            start = System.nanoTime();
            scan(s);
            System.out.println("Scan:  " + (System.nanoTime() - start));
        }
    }

    private static void tokenize(String s) {
        StreamTokenizer st = new StreamTokenizer(new StringReader(s));
        int token = 0;
        try {
            while ((token = st.nextToken())
                    == StreamTokenizer.TT_NUMBER) {
                double d = st.nval;
            }
        } catch (IOException e) {
            e.printStackTrace(System.err);
        }
    }

    private static void scan(String s) {
        Scanner scanner = new Scanner(s);
        while (scanner.hasNextDouble()) {
            double d = scanner.nextDouble();
        }
        scanner.close();
    }
}

[1]<http://download.oracle.com/javase/7/docs/api/java/io/StreamTokenizer.html>
[2]<http://stackoverflow.com/questions/2082174>
[3]<http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4079180>
[4]<http://www.resplendent.com/StlFileParser.java>

-- 
John B. Matthews
trashgod at gmail dot com
<http://sites.google.com/site/drjohnbmatthews>

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Thread

slow as molasses bob <bob@coolgroups.com> - 2011-10-04 02:16 -0700
  Re: slow as molasses Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-10-04 11:28 +0000
  Re: slow as molasses Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2011-10-04 07:47 -0700
  Re: slow as molasses Patricia Shanahan <pats@acm.org> - 2011-10-04 08:42 -0700
  Re: slow as molasses "John B. Matthews" <nospam@nospam.invalid> - 2011-10-04 13:30 -0400
    Re: slow as molasses bob <bob@coolgroups.com> - 2011-10-04 14:19 -0700

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