用Java写一个哈夫曼码的编/译码系统。

好的，下面是Java实现哈夫曼编/译码系统的代码示例：

import java.util.PriorityQueue;
import java.util.Scanner;

public class HuffmanCode {
    private static class Node implements Comparable<Node> {
        char ch;
        int freq;
        Node left, right;

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

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

        public int compareTo(Node that) {
            return this.freq - that.freq;
        }
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("请输入要编码的字符串：");
        String input = scanner.nextLine();

        int[] freq = new int[256];
        for (int i = 0; i < input.length(); i++) {
            freq[(int) input.charAt(i)]++;
        }

        Node root = buildHuffmanTree(freq);
        String[] codeTable = buildCodeTable(root);

        System.out.println("哈夫曼编码结果为：");
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < input.length(); i++) {
            sb.append(codeTable[(int) input.charAt(i)]);
        }
        System.out.println(sb.toString());

        System.out.println("哈夫曼解码结果为：");
        sb = new StringBuilder();
        Node node = root;
        for (int i = 0; i < sb.length(); i++) {
            char c = sb.charAt(i);
            if (c == '0') {
                node = node.left;
            } else {
                node = node.right;
            }
            if (node.isLeaf()) {
                sb.append(node.ch);
                node = root;
            }
        }
        System.out.println(sb.toString());
    }

    private static Node buildHuffmanTree(int[] freq) {
        PriorityQueue<Node> pq = new PriorityQueue<>();
        for (int i = 0; i < freq.length; i++) {
            if (freq[i] > 0) {
                pq.offer(new Node((char) i, freq[i], null, null));
            }
        }
        while (pq.size() > 1) {
            Node left = pq.poll();
            Node right = pq.poll();
            pq.offer(new Node('\0', left.freq + right.freq, left, right));
        }
        return pq.poll();
    }

    private static String[] buildCodeTable(Node root) {
        String[] codeTable = new String[256];
        buildCodeTable(root, "", codeTable);
        return codeTable;
    }

    private static void buildCodeTable(Node node, String code, String[] codeTable) {
        if (node.isLeaf()) {
            codeTable[node.ch] = code;
            return;
        }
        buildCodeTable(node.left, code + "0", codeTable);
        buildCodeTable(node.right, code + "1", codeTable);
    }
}

该程序实现了以下功能：

1. 输入一个字符串，统计每个字符出现的频率；
2. 基于字符频率构建哈夫曼树；
3. 根据哈夫曼树生成每个字符的编码表；
4. 对输入字符串进行编码，输出编码结果；
5. 对编码结果进行解码，输出解码结果。

该程序的时间复杂度为 O(nlogn)，其中n为字符串长度。