JAVA Write an application to test the HuffmanTree class Your

JAVA

Write an application to test the HuffmanTree class. Your application will need to read a text file and build a frequency table for the characters occurring in that file. Once that table is built create a Huffman code tree and then a string consisting of 0 and 1 characters that represents the code string for that file. Read that string back in and re-create the contents of the original file. Prompt the user for file name. Read the file, get the frequencies, create the huffman tree. Print the code for each character. Create the encoding for the file. Decode the file. Write the decoded file to another text file.

To get the ascii code of a character:

char somechar;//here you get somechar....reading from file...int i = Integer.parseInt(somechar);

Solution

package huffman; import java.util.*; abstract class HuffmanTree implements Comparable { public final int frequency; // the frequency of this tree public HuffmanTree(int freq) { frequency = freq; } // compares on the frequency public int compareTo(HuffmanTree tree) { return frequency - tree.frequency; } } class HuffmanLeaf extends HuffmanTree { public final char value; // the character this leaf represents public HuffmanLeaf(int freq, char val) { super(freq); value = val; } } class HuffmanNode extends HuffmanTree { public final HuffmanTree left, right; // subtrees public HuffmanNode(HuffmanTree l, HuffmanTree r) { super(l.frequency + r.frequency); left = l; right = r; } } public class Huffman { // input is an array of frequencies, indexed by character code public static HuffmanTree buildTree(int[] charFreqs, char[] test2) { PriorityQueue trees = new PriorityQueue(); // initially, we have a forest of leaves // one for each non-empty character for (int i = 0; i < charFreqs.length; i++) if (charFreqs[i] > 0) trees.offer(new HuffmanLeaf(charFreqs[i], test2[i])); assert trees.size() > 0; // loop until there is only one tree left while (trees.size() > 1) { // two trees with least frequency HuffmanTree a = trees.poll(); HuffmanTree b = trees.poll(); // put into new node and re-insert into queue trees.offer(new HuffmanNode(a, b)); } return trees.poll(); } public static void printCodes(HuffmanTree tree, StringBuffer prefix) { assert tree != null; if (tree instanceof HuffmanLeaf) { HuffmanLeaf leaf = (HuffmanLeaf)tree; // print out character, frequency, and code for this leaf (which is just the prefix) System.out.println(leaf.value + \"\\t\" + leaf.frequency + \"\\t\" + prefix); } else if (tree instanceof HuffmanNode) { HuffmanNode node = (HuffmanNode)tree; // traverse left prefix.append(\'0\'); printCodes(node.left, prefix); prefix.deleteCharAt(prefix.length()-1); // traverse right prefix.append(\'1\'); printCodes(node.right, prefix); prefix.deleteCharAt(prefix.length()-1); } } public static void main(String[] args) { //Symbols: String str = \"12345678\"; char[] test2 = str.toCharArray(); //Frequency (of the symbols above): int[] charFreqs = {36,18,12,9,7,6,5,4}; // build tree HuffmanTree tree = buildTree(charFreqs,test2); // print out results System.out.println(\"SYMBOL\\tFREQ\\tHUFFMAN CODE\"); printCodes(tree, new StringBuffer()); } }