CLI File Compression Utility (Huffman Coding)

import java.util.PriorityQueue;

class HuffmanNode implements Comparable<HuffmanNode> {
    int frequency;
    char data;
    HuffmanNode left, right;

    public int compareTo(HuffmanNode node) {
        return this.frequency - node.frequency;
    }
}

public class Huffman {
    public HuffmanNode buildTree(int[] charFreqs) {
        PriorityQueue<HuffmanNode> pq = new PriorityQueue<>();
        for (char i = 0; i < 256; i++) {
            if (charFreqs[i] > 0) {
                HuffmanNode node = new HuffmanNode();
                node.data = i;
                node.frequency = charFreqs[i];
                pq.add(node);
            }
        }
        while (pq.size() > 1) {
            HuffmanNode x = pq.peek(); pq.poll();
            HuffmanNode y = pq.peek(); pq.poll();
            HuffmanNode sum = new HuffmanNode();
            sum.frequency = x.frequency + y.frequency;
            sum.left = x;
            sum.right = y;
            pq.add(sum);
        }
        return pq.peek();
    }
}