Java file read problem

Question

Hi - I have a java problem. I am trying to read a txt file which has a variable number of integers per line, and for each line I need to sum every second integer! I am using scanner to read integers, but can't work out when a line is done. Can anyone help pls?

Answer 1

have a look at the BufferedReader class for reading a textfile and at the StringTokenizer class for splitting each line into strings.

String input;
BufferedReader br = new BufferedReader(new FileReader("foo.txt"));
while ((input = br.readLine()) != null) {
  input = input.trim();
  StringTokenizer str = new StringTokenizer(input);
  String text = str.nextToken(); //get your integers from this string
}

Answer 2

If I were you, I'd probably use FileUtils class from Apache Commons IO. The method readLines(File file) returns a List of Strings, one for each line. Then you can simply handle one line at a time.

Something like this:

    File file = new File("test.txt");
    List<String> lines = FileUtils.readLines(file);
    for (String line : lines) {
        // handle one line
    }

_{(Unfortunately Commons IO doesn't support generics, so the there would be an unchecked assignment warning when assigning to List<String>. To remedy that use either @SuppressWarnings, or just an untyped List and casting to Strings.)}

This is, perhaps, an example of a situation where one can apply "know and use the libraries" and skip writing some lower-level boilerplate code altogether.

Answer 3

or scrape from commons the essentials to both learn good technique and skip the jar:

import java.io.*;
import java.util.*;

class Test
{
    public static void main(final String[] args) 
    {

       File file = new File("Test.java"); 

       BufferedReader buffreader = null;
       String line = "";

        ArrayList<String> list = new ArrayList<String>(); 

        try 
            {
                buffreader = new BufferedReader( new FileReader(file) );
                line = buffreader.readLine();
                while (line != null) 
                {
                   line = buffreader.readLine();
                   //do something with line or:
                   list.add(line);
                }
             } catch (IOException ioe) 
             {
                    // ignore
             } finally 
             {
               try 
               {
                  if (buffreader != null) 
                  {
                     buffreader.close();
                  }
               } catch (IOException ioe) 
               {
                    // ignore
               }

            }

           //do something with list
           for (String text : list) 
           {       
               // handle one line
               System.out.println(text);       
           }

   }
}