Word frequency count example

With this example we are going to demonstrate how to count the frequency of words in a file. In short, to count the frequency of words in a file you should:

  • Create a new FileInputStream with a given String path by opening a connection to a file.
  • Get the FileChannel object associated with the FileInputStream, with getChannel() API method of FileInputStream.
  • Get the current size of this channel’s file, using size() API method of FileChannel.
  • Create a MappedByteBuffer, using map(MapMode mode, long position, long size) API method of FileChannel that maps a region of this channel’s file directly into memory.
  • Convert the byte buffer to character buffer. Create a new Charset for a specified charset name, using forName(String charsetName) API method of Charset and then a new CharsetDecoder, using newDecoder() API method of Charset. Then use decode(ByteBuffer in) API method of CharBuffer to decode the remaining content of a single input byte buffer into a newly-allocated character buffer.
  • Create a new word pattern and a new line pattern, by compiling given String regular expressions to a Pattern, using compile(string regex) API method of Pattern.
  • Match the line pattern to the buffer, using matcher(CharSequence input) API method of Pattern.
  • For each line get the line and the array of words in the line, using find() and group() API methods of Matcher, for the matcher created for the line pattern.
  • Then for each word get the word and add it in a TreeMap.

Let’s take a look at the code snippet that follows:

package com.javacodegeeks.snippets.core;
import java.nio.CharBuffer;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.charset.Charset;
import java.nio.charset.CharsetDecoder;
import java.util.Map;
import java.util.TreeMap;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class WordFreq {

    public static void main(String args[]) throws Exception {

  String filePath = "C:/Users/nikos7/Desktop/file.odt";

  // Map File from filename to byte buffer

  FileInputStream in = new FileInputStream(filePath);

  FileChannel filech = in.getChannel();

  int fileLen = (int) filech.size();

  MappedByteBuffer buf =, 0,


  // Convert to character buffer

  Charset chars = Charset.forName("ISO-8859-1");

  CharsetDecoder dec = chars.newDecoder();

  CharBuffer charBuf = dec.decode(buf);

  // Create line pattern

  Pattern linePatt = Pattern.compile(".*$", Pattern.MULTILINE);

  // Create word pattern

  Pattern wordBrkPatt = Pattern.compile("[\\p{Punct}\s}]");

  // Match line pattern to buffer

  Matcher lineM = linePatt.matcher(charBuf);

  Map m = new TreeMap();

  Integer one = new Integer(1);

  // For each line

  while (lineM.find()) {

// Get line

CharSequence lineSeq =;

// Get array of words on line

String words[] = wordBrkPatt.split(lineSeq);

// For each word

for (int i = 0, n = words.length; i < n; i++) {

    if (words[i].length() > 0) {

  Integer frequency = (Integer) m.get(words[i]);

  if (frequency == null) {

frequency = one;

  } else {

int value = frequency.intValue();

frequency = new Integer(value + 1);


  m.put(words[i], frequency);






WordPress=2, Working=1, Your=3, You’ll=1, a=136, able=1, about=8, above=2, absolutely=1, absurd=1, accept=.....

This was an example of how to count the frequency of words in a file in Java.

Ilias Tsagklis

Ilias is a software developer turned online entrepreneur. He is co-founder and Executive Editor at Java Code Geeks.
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