Use RandomAccessFile to save and read : RandomAccessFile « File « Java Tutorial

1. Java Tutorial
2. File
3. RandomAccessFile

import java.io.IOException;
import java.io.RandomAccessFile;

public class MainClass {
  public static void main(String[] args) throws IOException {
    RandomAccessFile rf = new RandomAccessFile("test.dat", "rw");
    for (int i = 0; i < 10; i++)
      rf.writeDouble(i * 1.414);
    rf.close();
    rf = new RandomAccessFile("test.dat", "rw");
    rf.seek(5 * 8);
    rf.writeDouble(47.0001);
    rf.close();
    rf = new RandomAccessFile("test.dat", "r");
    for (int i = 0; i < 10; i++)
      System.out.println("Value " + i + ": " + rf.readDouble());
    rf.close();

  }
}