read a specific line in an input file

[sara12345]

hello every one
how can I read a specific line in java for example line 7 in an input file I have used buffered reader but in this method I need to used line.nexline() and also I have used the LinenumberReader but in this method I can not give the line number I want to read

please help
thanks alot

[camickr]

In general you can't read the 7th line directlly. You need to create a loop to read the first 6 first.

However, if the length of each line is a "fixed length", then you can use RandomAccessFile and calculate the bytes to read manually at one time. I doubt you lines are fixed length so you will need to use the first solution.

[travishein]

You would need to read the lines before this line, and just ignore them or discard them, and for each line read, increment a counter, when the counter reaches the desired line, return that line, and of course checking to see if the file runs out before the requested line number has come up.

  /**
   * Reads a specific line from a text file in a platform neutral way, ignoring the lines before, and stopping after
   * reaching the desired line.
   * 
   * @param file
   *          The file to read from
   * @param lineNumber
   *          the line number to read.
   * @return the line that was requested, or null if the line number requested exceeds the number of lines in the file.
   * @throws IOException
   *           if an error was encountered while trying to read the file
   */
  public static String readSpecificLine(File file, int lineNumber) throws IOException {
    StringBuilder lineBuffer = new StringBuilder();
    String result = null;
    int lineCount = 0; // used to read until the specific line has been found.
    Reader reader = new InputStreamReader(new FileInputStream(file));
    try {
      char[] buffer = new char[4096];

      outer: for (int charsRead = reader.read(buffer); charsRead >= 0; charsRead = reader.read(buffer)) {
        for (int charIndex = 0; charIndex < charsRead; charIndex++) {
          char aChar = buffer[charIndex];
          switch (aChar) {
            case '\r': // ignore DOS end of lines (that will be before \n)
              break;
            case '\n':
              lineCount++;
              if (lineCount == lineNumber) {
                result = lineBuffer.toString();
                break outer;
              }
              else {
                // read a new line, but not interested in this line, discard
                lineBuffer = new StringBuilder();
              }
              break;
            default:
              lineBuffer.append(aChar);
              break;
          } // switch
        } // for (lineCount)
      } // for ( reading the file )
    }
    finally {
      try {
        reader.close();
      }
      catch (IOException ex) {
        // empty
      }
    }
    return result;
  }

I used this post on sun forums to read a new line in a platform independent manner:

Java Programming [Archive] - Fastest way to line count a file

[sara12345]

thanks alot for the replies I though that there is a way to read a line directly but now I have used line.nextLine() to go to specific line
thanks alot

[raqman]

http://java.sun.com/javase/6/docs/ap...l/Scanner.html can be used for scanning and processing many kinds of text input from a variety of sources.

http://java.sun.com/javase/6/docs/ap...redReader.html allows for buffered reading from an input stream and has a readLine() method that will read a single line from a stream (file in your case).

String.split() http://java.sun.com/javase/6/docs/ap...va.lang.String) splits a string by the supplied expression and returns the pieces as an array of strings.

The following code fragment opens a BufferedReader against a text file and reads each line.
Help with Code Tags Java Syntax (Toggle Plain Text)
try { BufferedReader reader = new BufferedReader(new FileReader("file.txt")); String line = null; while ((line = reader.readLine()) != null){ System.out.println(line); } } catch (Exception e){ e.printStackTrace(); } try {
BufferedReader reader = new BufferedReader(new FileReader("<strong class="highlight">file</strong>.txt"));

String <strong class="highlight">line</strong> = null;
while ((<strong class="highlight">line</strong> = reader.readLine()) != null){
System.out.println(<strong class="highlight">line</strong>);
}
} catch (Exception e){
e.printStackTrace();
}
With that as a starting point, see if you can get the elements into your array and post back if you run into problems.

[masternerdguy]

An idea is to load the entire file as a string and split the file by the linebreak character. Then just take the array[6] (the 6th index of the array) and you can access that line only.

[JosAH]

An idea is to load the entire file as a string and split the file by the linebreak character. Then just take the array[6] (the 6th index of the array) and you can access that line only.

Cute if your file has a zillion lines and you only need line number six.

kind regards,

Jos

[Supamagier]

An idea is to load the entire file as a string and split the file by the linebreak character. Then just take the array[6] (the 6th index of the array) and you can access that line only.

What the other guy said. :) Besides, array[6] is the 7th index (A)