HistNIOApp same as HistIOApp discussed in Chapter 9: Tech: Histogram I/O.
HistNIOTools -shown below.

import javax.swing.*;
import java.io.*;
import java.nio.*;
import java.nio.channels.*;

/**
  * This class contains several static methods used to
  * write and read histograms to disk files. It is identical
  * to HistIOTools class except for the following four
  * methods, which use NIO techniques:
  *
  * readFile(), writeFile()
  * packHistogram(), unpackHistogram()
  *
**/
public class HistNIOTools {

     ... This code section is identical to that in HistIOTools.

  /**
    * Use a FileChannel to read to read the histogram data
    * from the given file.
    *
    * @param file File object from which to locate file.
   **/
  public static Histogram readFile (File file) {

    try {

      FileChannel in_chan = new FileInputStream (file).getChannel ();

      // Assume histogram file sizes are always less than int max.
      int num_data = (int) in_chan.size ();

      ByteBuffer buffer = ByteBuffer.allocateDirect (num_data);
      in_chan.read (buffer);
      in_chan.close ();

      return unpackHistogram (buffer);

    } catch (IOException ioe ) {
      JOptionPane.showMessageDialog (
            null,
            "Error in reading data!!\n\r"+ioe,
            "Histogram File Read Error",
            JOptionPane.ERROR_MESSAGE);
      return null;
    }
  } // readFile

  /**
    * Use a FileChannel to write a ByteBuffer containing the
    * histogram data to the given file.
    *
    * @param file File object for the file to receive the histogram data.
   **/
  public static boolean writeFile (File file, Histogram histogram) {

    ByteBuffer buffer = packHistogram (histogram);
    try {
      FileChannel out_chan = new FileOutputStream (file).getChannel();
      out_chan.write (buffer);
      out_chan.close ();
    }
    catch  (IOException ioe) {
      JOptionPane.showMessageDialog (
                  null,
                  "Error in writing data!!\n\r"+ioe,
                  "Histogram File Save Error",
                  JOptionPane.ERROR_MESSAGE);
      return false;
    }
    return true;
  } // writeFile

  /**
    * Convert histogram data to a byte array
    * for storage using a byte array stream.
    *
    * @param hist Histogram object containing data to be packed.
   **/
  public static ByteBuffer packHistogram (Histogram hist) {

    // The write methods can throw IOExceptions so must set up
    // to catch them
    try {

      // Need the length of the title
      int num_chars_title = hist.getTitle ().length ();

      // The length of the label
      int num_chars_label = hist.getXLabel ().length ();

      // And the bin array
      int [] bins = hist.getBins ();

      // Add up total buffer size. This include 3*4 = 12 for the
      // title, label and bin array sizes. Also,
      //   under + overflow ints plus upper + lower range doubles = 24
      int total_byte_size = 12 + num_chars_title*2 + num_chars_label*2 +
                            bins.length*4 + 24;

      ByteBuffer buffer = ByteBuffer.allocateDirect (total_byte_size);

      buffer.putInt (num_chars_title);
      CharBuffer char_buffer = CharBuffer.wrap (hist.getTitle ());
      (buffer.asCharBuffer ()).put (char_buffer);

      buffer.putInt (num_chars_label);
      char_buffer = CharBuffer.wrap (hist.getXLabel ());
      (buffer.asCharBuffer ()).put (char_buffer);

      buffer.putInt (bins.length);
      IntBuffer int_buffer = IntBuffer.wrap (bins);
      (buffer.asIntBuffer ()).put (int_buffer);

      // Save underflow value.
      buffer.putInt (hist.getValue (-1));
      // Save overflow value.
      buffer.putInt (hist.getValue (bins.length));

      // Write the lower and upper range values
      buffer.putDouble (hist.getLo ());
      buffer.putDouble (hist.getHi ());

      return buffer;

    }
    catch (BufferOverflowException e) {
      JOptionPane.showMessageDialog (
            null,
            "Error in packing data!!\n\r" + e,
            "Histogram Data Error",
            JOptionPane.ERROR_MESSAGE);
       return null;
    }
  } // packHistogram

  /** Re-build a histogram from a byte array. **/
  public static Histogram unpackHistogram (ByteBuffer hist_buffer){

    // The read  methods can throw IOExceptions so must set up
    // to catch them
    try {
      // First read the characters for the title
      int num_chars = hist_buffer.getInt ();
      char [] char_array = new char[num_chars];
      for (int i=0; i < num_chars; i++) {
        char_array[i] = hist_buffer.getChar ();
      }

      String title = String.valueOf (char_array);

      // First read the characters for the horizontal label
      num_chars = hist_buffer.getInt ();
      char_array = new char[num_chars];
      for (int i=0; i < num_chars; i++) {
        char_array[i] = hist_buffer.getChar ();
      }

      String x_label = String.valueOf (char_array);

      // Get the bin data
      int num_bins = hist_buffer.getInt ();
      int [] bins = new int[num_bins];
      for (int i=0; i < num_bins; i++)  {
          bins[i] = hist_buffer.getInt ();
      }

      int under_flows = hist_buffer.getInt ();
      int over_flows  = hist_buffer.getInt ();

      double lo = hist_buffer.getDouble ();
      double hi = hist_buffer.getDouble ();

      // Create a histogram with
      Histogram hist = new Histogram (title, x_label, num_bins, lo, hi);
      // Pack the rest of the data.
      hist.pack (bins, under_flows, over_flows, lo, hi);

      return hist;

    } catch (BufferUnderflowException e) {
       JOptionPane.showMessageDialog (
            null,
            "Error in unpacking data!!\n\r" + e,
            "Histogram Data Error",
            JOptionPane.ERROR_MESSAGE);
       return null;
    }
  } // unpackHistogram

     ... Rest of code is identical to that in HistIOTools.

} // class HistNIOTools