import java.nio.file.*;
import java.nio.*;
import java.io.*;

public class StreamOutputToFile {

  public static void main(String[] args) {
    final int count = 50;                                              // Number of values
    long[] fiboNumbers = {0L,0L};                                      // Array of 2 elements
    int index = 0;                                                     // Index to fibonumbers
    ByteBuffer buf = ByteBuffer.allocate(count*8);                     // Buffer for output
    LongBuffer longBuf = buf.asLongBuffer();                           // View buffer for type long
    Path file = Paths.get("D:/Junk/fibonnaci.bin");
    try {
      // Create parent directory if it doesn't exist
      Files.createDirectories(file.getParent());
    } catch(IOException e) {
      System.err.println("Error creating directory: " + file.getParent());
      e.printStackTrace();
    }

    try(BufferedOutputStream fileOut = new BufferedOutputStream(Files.newOutputStream(file))){
      // Generate Fibonacci numbers in buffer
      for(int i = 0 ; i < count ; ++i) {
        if(i < 2)
          fiboNumbers[index] = i;
        else
          fiboNumbers[index] = fiboNumbers[0] + fiboNumbers[1];
        longBuf.put(fiboNumbers[index]);
        index = ++index%2;
      }
    // Write the numbers to the file
    fileOut.write(buf.array(), 0, buf.capacity());
    System.out.println("File written.");
    } catch(IOException e) {
      System.err.println("Error writing file: " + file);
      e.printStackTrace();
    }
  }
}