import java.io.*;

/**
  * Use RandomAccessFile to write a number into a file.
  * Command line specifies the single integer value to
  * write, the position in the file where it is to be
  * written, and the name of the file, which should contain
  * a series of integer values. The position will be in
  * terms of integer values, not bytes. The file will be
  * created if it doesn't exist already.
**/
public class RandomFileTest  {


  public static void main (String [] args) {

    int value = 0;
    long position = 0;

    if (args.length < 3) {
      System.out.println ("Usage: java RandomFileTest value position filename");
      System.exit(0);
    }

    try {
      value = Integer.parseInt (args[0]);
    }
    catch (NumberFormatException nfe) {
      System.out.println ("Bad number value!");
      System.out.println ("Usage: java RandomFileTest value position filename");
      System.exit (0);
    }

    // Check
    try {
      position = Long.parseLong (args[1]);
      // Treat number as absolute value.
      if (position < 0) position = -position;
      position = 4*position; // 4 bytes per integer.
    }
    catch (NumberFormatException nfe) {
      System.out.println ("Bad position value!");
      System.out.println ("Usage: java RandomFileTest value position filename");
      System.exit (0);
    }

    RandomAccessFile file = null;
    try {
      file = new RandomAccessFile (args[2], "rw");
    }
    catch (FileNotFoundException ffe) {
      System.out.println("File not found. Will create it.");
    }

    try {

      // Append if position beyond the end of the file.
      if (position > 0 && position >= file.length ()) {
        position = file.length ();
      }

      // Move to the desired position and write the number.
      file.seek (position);
      file.writeInt (value);

      // Move back to the start of the file and print it out
      file.seek (0);
      int num_entries = (int)(file.length () / 4);
      for (int i=0; i < num_entries; i++) {
        System.out.printf ("%10d", file.readInt ());
        if (i != 0 && (i%6) == 0) System.out.println();
      }
      System.out.println();

    }
    catch (IOException ioe) {
      System.out.println ("IO Exception = " + ioe);
    }
  } // main

} // RandomFileTest