write a java program related to Huffman coding. Solution The Java program for Huffman coding is as below: public final class Huffman { private Huffman() {}; private static class HuffmanNode { char ch; int frequency; HuffmanNode left; HuffmanNode right; HuffmanNode(char ch, int frequency, HuffmanNode left, HuffmanNode right) { this.ch = ch; this.frequency = frequency; this.left = left; this.right = right; } } private static class HuffManComparator implements Comparator { @Override public int compare(HuffmanNode node1, HuffmanNode node2) { return node1.frequency - node2.frequency; } } public static void compress(String sentence) throws FileNotFoundException, IOException { if (sentence == null) { throw new NullPointerException(\"Input sentence cannot be null.\"); } if (sentence.length() == 0) { throw new IllegalArgumentException(\"The string should atleast have 1 character.\"); } final Map charFreq = getCharFrequency(sentence); final HuffmanNode root = buildTree(charFreq); final Map charCode = generateCodes(charFreq.keySet(), root); final String encodedMessage = encodeMessage(charCode, sentence); serializeTree(root); serializeMessage(encodedMessage); } private static Map getCharFrequency(String sentence) { final Map map = new HashMap(); for (int i = 0; i < sentence.length(); i++) { char ch = sentence.charAt(i); if (!map.containsKey(ch)) { map.put(ch, 1); } else { int val = map.get(ch); map.put(ch, ++val); } } return map; } private static HuffmanNode buildTree(Map map) { final Queue nodeQueue = createNodeQueue(map); while (nodeQueue.size() > 1) { final HuffmanNode node1 = nodeQueue.remove(); final HuffmanNode node2 = nodeQueue.remove(); HuffmanNode node = new HuffmanNode(\'\\0\', node1.frequency + node2.frequency, node1, node2); nodeQueue.add(node); } return nodeQueue.remove(); } private static Queue createNodeQueue(Map map) { final Queue pq = new PriorityQueue(11, new HuffManComparator()); for (Entry entry : map.entrySet()) { pq.add(new HuffmanNode(entry.getKey(), entry.getValue(), null, null)); } return pq; } private static Map generateCodes(Set chars, HuffmanNode node) { final Map map = new HashMap(); doGenerateCode(node, map, \"\"); return map; } private static void doGenerateCode(HuffmanNode node, Map map, String s) { if (node.left == null && node.right == null) { map.put(node.ch, s); return; } doGenerateCode(node.left, map, s + \'0\'); doGenerateCode(node.right, map, s + \'1\' ); } private static String encodeMessage(Map charCode, String sentence) { final StringBuilder stringBuilder = new StringBuilder(); for (int i = 0; i < sentence.length(); i++) { stringBuilder.append(charCode.get(sentence.charAt(i))); } return stringBuilder.toString(); } private static void serializeTree(HuffmanNode node) throws FileNotFoundException, IOException { final BitSet bitSet = new BitSet(); try (ObjectOutputStream oosTree = new ObjectOutputStream(new FileOutputStream(\"/Users/ap/Desktop/tree\"))) { try (ObjectOutputStream oosChar = new ObjectOutputStream(new F.

1. write a java program related to Huffman coding.
Solution
The Java program for Huffman coding is as below:
public final class Huffman
{
private Huffman() {};
private static class HuffmanNode
{
char ch;
int frequency;
HuffmanNode left;
HuffmanNode right;
HuffmanNode(char ch, int frequency, HuffmanNode left, HuffmanNode right) {
this.ch = ch;
this.frequency = frequency;
this.left = left;
this.right = right;
}
}
private static class HuffManComparator implements Comparator
{
@Override
public int compare(HuffmanNode node1, HuffmanNode node2)
{
return node1.frequency - node2.frequency;
}
}
public static void compress(String sentence) throws FileNotFoundException, IOException {
if (sentence == null) {
throw new NullPointerException("Input sentence cannot be null.");
}
if (sentence.length() == 0)
{

2. throw new IllegalArgumentException("The string should atleast have 1 character.");
}
final Map charFreq = getCharFrequency(sentence);
final HuffmanNode root = buildTree(charFreq);
final Map charCode = generateCodes(charFreq.keySet(), root);
final String encodedMessage = encodeMessage(charCode, sentence);
serializeTree(root);
serializeMessage(encodedMessage);
}
private static Map getCharFrequency(String sentence)
{
final Map map = new HashMap();
for (int i = 0; i < sentence.length(); i++) {
char ch = sentence.charAt(i);
if (!map.containsKey(ch))
{
map.put(ch, 1);
}
else
{
int val = map.get(ch);
map.put(ch, ++val);
}
}
return map;
}
private static HuffmanNode buildTree(Map map)
{
final Queue nodeQueue = createNodeQueue(map);
while (nodeQueue.size() > 1)
{
final HuffmanNode node1 = nodeQueue.remove();
final HuffmanNode node2 = nodeQueue.remove();
HuffmanNode node = new HuffmanNode('0', node1.frequency + node2.frequency, node1,
node2);
nodeQueue.add(node);

3. }
return nodeQueue.remove();
}
private static Queue createNodeQueue(Map map) {
final Queue pq = new PriorityQueue(11, new HuffManComparator());
for (Entry entry : map.entrySet())
{
pq.add(new HuffmanNode(entry.getKey(), entry.getValue(), null, null));
}
return pq;
}
private static Map generateCodes(Set chars, HuffmanNode node) {
final Map map = new HashMap();
doGenerateCode(node, map, "");
return map;
}
private static void doGenerateCode(HuffmanNode node, Map map, String s)
{
if (node.left == null && node.right == null)
{
map.put(node.ch, s);
return;
}
doGenerateCode(node.left, map, s + '0');
doGenerateCode(node.right, map, s + '1' );
}
private static String encodeMessage(Map charCode, String sentence) {
final StringBuilder stringBuilder = new StringBuilder();
for (int i = 0; i < sentence.length(); i++) {
stringBuilder.append(charCode.get(sentence.charAt(i)));
}
return stringBuilder.toString();
}
private static void serializeTree(HuffmanNode node) throws FileNotFoundException,
IOException {
final BitSet bitSet = new BitSet();

4. try (ObjectOutputStream oosTree = new ObjectOutputStream(new
FileOutputStream("/Users/ap/Desktop/tree")))
{
try (ObjectOutputStream oosChar = new ObjectOutputStream(new
FileOutputStream("/Users/ap/Desktop/char")))
{
IntObject o = new IntObject();
preOrder(node, oosChar, bitSet, o);
bitSet.set(o.bitPosition, true);
oosTree.writeObject(bitSet);
}
}
}
private static class IntObject
{
int bitPosition;
}
private static void preOrder(HuffmanNode node, ObjectOutputStream oosChar, BitSet bitSet,
IntObject intObject) throws IOException {
if (node.left == null && node.right == null) {
bitSet.set(intObject.bitPosition++, false);
oosChar.writeChar(node.ch);
return;
}
bitSet.set(intObject.bitPosition++, true);
preOrder(node.left, oosChar, bitSet, intObject);
bitSet.set(intObject.bitPosition++, true);
preOrder(node.right, oosChar, bitSet, intObject);
}
private static void serializeMessage(String message) throws IOException {
final BitSet bitSet = getBitSet(message);
try (ObjectOutputStream oos = new ObjectOutputStream(new
FileOutputStream("/Users/ap/Desktop/encodedMessage"))){
oos.writeObject(bitSet);
}
}

5. private static BitSet getBitSet(String message) {
final BitSet bitSet = new BitSet();
int i = 0;
for (i = 0; i < message.length(); i++) {
if (message.charAt(i) == '0') {
bitSet.set(i, false);
}
else
{
bitSet.set(i, true);
}
}
bitSet.set(i, true);
return bitSet;
}
public static String expand() throws FileNotFoundException, ClassNotFoundException,
IOException {
final HuffmanNode root = deserializeTree();
return decodeMessage(root);
}
private static HuffmanNode deserializeTree() throws FileNotFoundException, IOException,
ClassNotFoundException {
try (ObjectInputStream oisBranch = new ObjectInputStream(new
FileInputStream("/Users/ap/Desktop/tree"))) {
try (ObjectInputStream oisChar = new ObjectInputStream(new
FileInputStream("/Users/ap/Desktop/char"))) {
final BitSet bitSet = (BitSet) oisBranch.readObject();
return preOrder(bitSet, oisChar, new IntObject());
}
}
}
private static HuffmanNode preOrder(BitSet bitSet, ObjectInputStream oisChar, IntObject o)
throws IOException {
final HuffmanNode node = new HuffmanNode('0', 0, null, null);
if (!bitSet.get(o.bitPosition)) {
o.bitPosition++;

6. node.ch = oisChar.readChar();
return node;
}
o.bitPosition = o.bitPosition + 1;
node.left = preOrder(bitSet, oisChar, o);
o.bitPosition = o.bitPosition + 1;
node.right = preOrder(bitSet, oisChar, o);
return node;
}
private static String decodeMessage(HuffmanNode node) throws FileNotFoundException,
IOException, ClassNotFoundException {
try (ObjectInputStream ois = new ObjectInputStream(new
FileInputStream("/Users/ameya.patil/Desktop/encodedMessage"))) {
final BitSet bitSet = (BitSet) ois.readObject();
final StringBuilder stringBuilder = new StringBuilder();
for (int i = 0; i < (bitSet.length() - 1);) {
HuffmanNode temp = node;
while (temp.left != null) {
if (!bitSet.get(i)) {
temp = temp.left;
} else {
temp = temp.right;
}
i = i + 1;
}
stringBuilder.append(temp.ch);
}
return stringBuilder.toString();
}
}
public static void main(String[] args) throws FileNotFoundException, IOException,
ClassNotFoundException {
Huffman.compress("some");
Assert.assertEquals("some", Huffman.expand());
Huffman.compress("someday");
Assert.assertEquals("someday", Huffman.expand());

7. Huffman.compress("some some#");
Assert.assertEquals("some some#", Huffman.expand());
Huffman.compress("someday someday&");
Assert.assertEquals("someday someday&", Huffman.expand());
}
}