CODEWITHSUNDEEP
javafileinputbufferedreader
paul_1991
paul_1991

Reputation: 231

BufferedReader pointer

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.

Upvotes: 0

Views: 6467

Answers (3)

corlettk
corlettk

Reputation: 13574

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.

Upvotes: 1

Peter Knego
Peter Knego

Reputation: 80340

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.

Upvotes: 0

Howard
Howard

Reputation: 39197

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();

Upvotes: 0

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