用Java写文本文件压缩和解压，采用哈夫曼编码，并给出代码注释

好的，我可以为您提供相关的Java代码，如下所示：

首先，我们需要实现哈夫曼编码的相关功能，包括建立哈夫曼树、生成哈夫曼编码表等。以下是哈夫曼编码的实现代码：

import java.util.Map;
import java.util.HashMap;
import java.util.PriorityQueue;

public class HuffmanCoding {

    private static class TreeNode implements Comparable<TreeNode> {
        private final char ch;
        private final int freq;
        private final TreeNode left, right;

        TreeNode(char ch, int freq, TreeNode left, TreeNode right) {
            this.ch = ch;
            this.freq = freq;
            this.left = left;
            this.right = right;
        }

        public boolean isLeaf() {
            return left == null && right == null;
        }

        @Override
        public int compareTo(TreeNode other) {
            return Integer.compare(freq, other.freq);
        }
    }

    public static Map<Character, String> buildHuffmanTable(String input) {
        int[] freq = new int[256];
        for (char ch : input.toCharArray()) {
            freq[ch]++;
        }

        PriorityQueue<TreeNode> pq = new PriorityQueue<>();
        for (char i = 0; i < freq.length; i++) {
            if (freq[i] > 0) {
                pq.add(new TreeNode(i, freq[i], null, null));
            }
        }

        while (pq.size() > 1) {
            TreeNode left = pq.poll();
            TreeNode right = pq.poll();
            pq.add(new TreeNode('\0', left.freq + right.freq, left, right));
        }

        Map<Character, String> huffmanTable = new HashMap<>();
        buildHuffmanTable(huffmanTable, pq.peek(), "");
        return huffmanTable;
    }

    private static void buildHuffmanTable(Map<Character, String> table, TreeNode node, String code) {
        if (node.isLeaf()) {
            table.put(node.ch, code);
        } else {
            buildHuffmanTable(table, node.left, code + '0');
            buildHuffmanTable(table, node.right, code + '1');
        }
    }
}

接下来我们需要使用上述哈夫曼编码实现文本文件的压缩和解压。以下是压缩和解压的代码实现，其中对于输入的文件路径和输出的文件路径需要您自行指定：

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.Map;

public class HuffmanCompression {

    public static void compress(String inputFilePath, String outputFilePath) throws IOException {
        FileInputStream in = new FileInputStream(inputFilePath);
        FileOutputStream out = new FileOutputStream(outputFilePath);

        StringBuilder input = new StringBuilder();
        int bytesRead;
        byte[] buffer = new byte[1024];
        while ((bytesRead = in.read(buffer)) != -1) {
            for (int i = 0; i < bytesRead; i++) {
                input.append((char) buffer[i]);
            }
        }
        in.close();

        Map<Character, String> huffmanTable = HuffmanCoding.buildHuffmanTable(input.toString());

        StringBuilder encoded = new StringBuilder();
        for (char ch : input.toString().toCharArray()) {
            encoded.append(huffmanTable.get(ch));
        }

        while (encoded.length() % 8 != 0) {
            encoded.append('0');
        }

        for (int i = 0; i < encoded.length(); i += 8) {
            String byteStr = encoded.substring(i, i + 8);
            int b = Integer.parseInt(byteStr, 2);
            out.write((byte) b);
        }
        out.close();
    }

    public static void decompress(String inputFilePath, String outputFilePath) throws IOException {
        FileInputStream in = new FileInputStream(inputFilePath);
        FileOutputStream out = new FileOutputStream(outputFilePath);

        StringBuilder encoded = new StringBuilder();
        int bytesRead;
        byte[] buffer = new byte[1024];
        while ((bytesRead = in.read(buffer)) != -1) {
            for (int i = 0; i < bytesRead; i++) {
                String byteStr = Integer.toBinaryString(256 + (int) buffer[i]);
                encoded.append(byteStr.substring(byteStr.length() - 8));
            }
        }
        in.close();

        Map<String, Character> huffmanTable = new HashMap<>();
        for (Map.Entry<Character, String> entry : HuffmanCoding.buildHuffmanTable(encoded.toString()).entrySet()) {
            huffmanTable.put(entry.getValue(), entry.getKey());
        }

        StringBuilder decoded = new StringBuilder();
        String key = "";
        for (char bit : encoded.toString().toCharArray()) {
            key += bit;
            if (huffmanTable.containsKey(key)) {
                decoded.append(huffmanTable.get(key));
                key = "";
            }
        }

        out.write(decoded.toString().getBytes());
        out.close();
    }
}

最后，我们可以调用上述的压缩和解压函数进行压缩和解压操作，如下所示：

public static void main(String[] args) throws IOException {
    HuffmanCompression.compress("input.txt", "compressed.bin");
    HuffmanCompression.decompress("compressed.bin", "output.txt");
}

注意，上述代码中的 "input.txt" 和 "output.txt" 分别是输入文件和输出文件的路径，您需要根据具体情况进行修改。