BufferedReader pointer

Question

I have the following code but I don't understand how I can reset the pointer to the starter position:

BufferedReader inp=new BufferedReader(new FileReader(file));
Scanner leggi=new Scanner(inp);
for(int i=0;i<nwords;i++){
  while(leggi.hasNext()) 
    if(leggi.next().equals(args[i+2])) 
      occorrenze[i]=occorrenze[i]+1;
}
inp.close();

I tried

inp.mark(0);
inp.reset();

with no results.

possible duplicate of [Java BufferedReader back to the top of a text file?](http://stackoverflow.com/questions/262618/java-bufferedreader-back-to-the-top-of-a-text-file) — jmj, Apr 30 '11 at 10:41
Please see my revised Answer below. I added some code to my Answer, but SOF doesn't notify you of edits, but does notify you of new comments; hence this comment ;-) — corlettk, Apr 30 '11 at 11:15

score 1 · Accepted Answer · edited May 23 '17 at 11:47

Paul,

I suggest you read through this old thread: Java BufferedReader back to the top of a text file?.

Personally I prefer Jon Skeet's response, which boils down to "Don't bother [unless you MUST]."

Cheers. Keith.

EDIT: Also you should ALLWAYS close that input file, even if you hit an Exception. The finally block is perfect for this.

EDIT2:

Hope you're still with us.

Here's my attempt, and FWIW, you DON'T need to reset the input-file, you just need to transpose your while and for loops.

package forums;

import java.util.Scanner;
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

public class WordOccurrenceCount
{
  public static void main(String[] args) {
    try {
      String[] words = { "and", "is", "a", "the", "of", "as" };
      int[] occurrences = readOccurrences("C:/tmp/prose.txt", words);
      for ( int i=0; i<words.length; i++ ) {
        System.out.println(words[i] + " " + occurrences[i]);
      }
    } catch (Exception e) {
      e.printStackTrace();
    }
  }

  private static final int[] readOccurrences(String filename, String... words) 
    throws IOException
  {
    int[] occurrences = new int[words.length];
    BufferedReader reader = null;
    try {
      reader = new BufferedReader(new FileReader(filename));
      Scanner scanner = new Scanner(reader);
      while ( scanner.hasNext() ) {
        String word = scanner.next();
        for ( int i=0; i<words.length; i++ ) {
          if ( words[i].equals(word) ) {
            occurrences[i]++;
          }
        }
      }
    } finally {
      if(reader!=null) reader.close();
    }
    return occurrences;
  }
}

And BTW, java.util.Map is perfect for building a frequency table... Parallel arrays are just SOOOOO 90's. The "default" implementation of Map is the HashMap class... By default I mean use HashMap whenever you need a Map, unless you've got a good reason to use something else, which won't be often. HashMap is generally the best allround performer.

Paul, no sorry, you've still got the same problem... Please see my edits above. As a general rule, performance dictates that we not re-read a file any more than necessarym, even if it is small enough to sit in the cache. Another general rule when dealing with loops-within-loops is "do the smaller part inside". Does that make sense to you? — corlettk, Apr 30 '11 at 11:22

score 0 · Answer 2 · answered Apr 30 '11 at 10:41

You have two options:

reset the FileReader (FieldReader.reset) instead and create a new bufferedreader.
use mark functionaliy (try BufferedReader.markSupported)

I think what you tried is to call mark after you read the input. Instead do the following:

inp.mark(readAheadLimit);    
// .... all your code processing input
inp.reset();

score 0 · Answer 3 · answered Apr 30 '11 at 10:42

0

mark(int readAheadLimit) takes a readAheadLimit parameter.

You should not set the readAheadLimit to 0. Try using a meaningful number that is larger than number of bytes you read in an iteration.

answered Apr 30 '11 at 10:42

Peter Knego

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BufferedReader pointer

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