InputStreamReader read = new InputStreamReader(new FileInputStream(file), encoding);

This line of code creates a new InputStreamReader object that takes in a FileInputStream object and an encoding parameter. The FileInputStream object represents a file input stream that reads bytes from the specified file. The InputStreamReader object then converts those bytes into characters using the specified encoding.

The resulting InputStreamReader object can be used to read the contents of the file as characters, rather than bytes. This is useful when working with text files, as it allows you to read and manipulate the contents of the file as strings.

相关问题

InputStreamReader

The InputStreamReader class is a subclass of the Reader class in Java. It reads bytes from an InputStream and decodes them into characters using a specified character encoding. The decoded characters are then made available to the programmer as a stream of characters.

The InputStreamReader class is used when we want to read data from an InputStream and process it as text. It provides a convenient way to convert binary data into text data.

Here is an example of using an InputStreamReader to read data from an InputStream:

InputStream inputStream = new FileInputStream("data.txt");
InputStreamReader reader = new InputStreamReader(inputStream, "UTF-8");

int data = reader.read();
while (data != -1) {
    char ch = (char) data;
    System.out.print(ch);
    data = reader.read();
}

reader.close();
inputStream.close();

In this example, we create an InputStream from a file called "data.txt". We then create an InputStreamReader using the UTF-8 character encoding. We read data from the InputStreamReader one character at a time using the read() method. The read() method returns -1 when the end of the stream is reached. Finally, we close the InputStreamReader and the InputStream.

用java编写哈夫曼编码实现:(1)I：初始化(Initialization)。从终端读入字符集大小n，以及n个字符和n个权值，建立哈夫曼树，并将它存于文件hfmTree中。 (2)E：编码(Encoding)。利用已建好的哈夫曼树(如不在内存，则从文件hfmTree中读人)，对文件ToBeTran中的正文进行编码，然后将结果存入文件CodeFile中。 (3)D：译码(Decoding)。利用已建好的哈夫曼树将文件 CodeFile中的代码进行译码，结果存入文件TextFile中。 (4)P：打印代码文件(Print)。将文件CodeFile以紧凑格式显示在终端上，每行50个代码。同时将此字符形式的编码文件写入文件CodePrin中。 (5)T：打印哈夫曼树(Tree printing)。将已在内存中的哈夫曼树以直观的方式(树或凹入表形式)显示在终端上，同时将此字符形式的哈夫曼树写入文件TreePrint中。 【测试数据】 用下表给出的字符集和频度的实际统计数据建立哈夫曼树，并实现以下报文的编码和译码："THIS PROGRAM IS MY FAVORITE"。 字符 A B C D E F G HI J K L M 频度186 64 13 22 32 103 21 15 47 57 1 5 32 20 字符N 0 P Q R S T U V WX Y 频度57 63 15 1 48 51 80 23 8 18 1 16 1

以下是用Java编写的哈夫曼编码实现：

HuffmanNode.java

public class HuffmanNode implements Comparable<HuffmanNode> {
    char ch;
    int freq;
    HuffmanNode left, right;

    public HuffmanNode(char ch, int freq, HuffmanNode left, HuffmanNode 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(HuffmanNode o) {
        return freq - o.freq;
    }
}

HuffmanTree.java

import java.io.*;
import java.util.*;

public class HuffmanTree {
    private HuffmanNode root;

    public void initialize() throws IOException {
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));

        // 读入字符集大小和字符频率
        int n = Integer.parseInt(reader.readLine());
        char[] chars = new char[n];
        int[] freqs = new int[n];
        for (int i = 0; i < n; i++) {
            String[] parts = reader.readLine().split(" ");
            chars[i] = parts[0].charAt(0);
            freqs[i] = Integer.parseInt(parts[1]);
        }

        // 建立哈夫曼树
        PriorityQueue<HuffmanNode> pq = new PriorityQueue<>();
        for (int i = 0; i < n; i++) {
            pq.offer(new HuffmanNode(chars[i], freqs[i], null, null));
        }
        while (pq.size() > 1) {
            HuffmanNode left = pq.poll();
            HuffmanNode right = pq.poll();
            pq.offer(new HuffmanNode('\0', left.freq + right.freq, left, right));
        }
        root = pq.poll();

        // 将哈夫曼树存入文件
        try (ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream("hfmTree"))) {
            out.writeObject(root);
        }
    }

    public void encoding() throws IOException, ClassNotFoundException {
        // 读入哈夫曼树
        try (ObjectInputStream in = new ObjectInputStream(new FileInputStream("hfmTree"))) {
            root = (HuffmanNode) in.readObject();
        }

        // 编码文本文件
        BufferedReader reader = new BufferedReader(new FileReader("ToBeTran"));
        BitOutputStream out = new BitOutputStream(new FileOutputStream("CodeFile"));
        String line;
        while ((line = reader.readLine()) != null) {
            for (int i = 0; i < line.length(); i++) {
                char ch = line.charAt(i);
                String code = getCode(ch);
                for (int j = 0; j < code.length(); j++) {
                    out.writeBit(code.charAt(j) == '1' ? 1 : 0);
                }
            }
        }
        reader.close();
        out.close();
    }

    public void decoding() throws IOException, ClassNotFoundException {
        // 读入哈夫曼树
        try (ObjectInputStream in = new ObjectInputStream(new FileInputStream("hfmTree"))) {
            root = (HuffmanNode) in.readObject();
        }

        // 译码代码文件
        BitInputStream in = new BitInputStream(new FileInputStream("CodeFile"));
        BufferedWriter writer = new BufferedWriter(new FileWriter("TextFile"));
        HuffmanNode node = root;
        while (true) {
            int bit = in.readBit();
            if (bit < 0) break;
            if (bit == 0) node = node.left;
            else node = node.right;
            if (node.isLeaf()) {
                writer.write(node.ch);
                node = root;
            }
        }
        in.close();
        writer.close();
    }

    public void printingCodeFile() throws IOException {
        BufferedReader reader = new BufferedReader(new FileReader("CodeFile"));
        BufferedWriter writer = new BufferedWriter(new FileWriter("CodePrin"));
        int count = 0;
        int c;
        while ((c = reader.read()) != -1) {
            writer.write(c);
            count++;
            if (count == 50) {
                writer.newLine();
                count = 0;
            }
        }
        reader.close();
        writer.close();
    }

    public void printingHuffmanTree() throws IOException, ClassNotFoundException {
        // 读入哈夫曼树
        try (ObjectInputStream in = new ObjectInputStream(new FileInputStream("hfmTree"))) {
            root = (HuffmanNode) in.readObject();
        }

        // 打印哈夫曼树
        BufferedWriter writer = new BufferedWriter(new FileWriter("TreePrint"));
        printHuffmanTree(root, "", writer);
        writer.close();
    }

    private String getCode(char ch) {
        StringBuilder sb = new StringBuilder();
        getCode(root, ch, sb);
        return sb.toString();
    }

    private void getCode(HuffmanNode node, char ch, StringBuilder sb) {
        if (node == null) return;
        if (node.isLeaf() && node.ch == ch) return;
        if (node.left != null) {
            getCode(node.left, ch, sb);
            if (sb.length() > 0) sb.append('0');
        }
        if (node.right != null) {
            getCode(node.right, ch, sb);
            if (sb.length() > 0) sb.append('1');
        }
        if (sb.length() > 0 && sb.charAt(sb.length() - 1) != '0') sb.deleteCharAt(sb.length() - 1);
    }

    private void printHuffmanTree(HuffmanNode node, String indent, BufferedWriter writer) throws IOException {
        if (node == null) return;
        writer.write(indent);
        if (node.isLeaf()) {
            writer.write(node.ch + "\n");
        } else {
            writer.write("-\n");
            printHuffmanTree(node.left, indent + "  |", writer);
            printHuffmanTree(node.right, indent + "   ", writer);
        }
    }

    private static class BitOutputStream {
        private OutputStream out;
        private int buffer;
        private int count;

        public BitOutputStream(OutputStream out) {
            this.out = out;
            buffer = 0;
            count = 0;
        }

        public void writeBit(int bit) throws IOException {
            buffer <<= 1;
            if (bit == 1) buffer |= 1;
            count++;
            if (count == 8) {
                out.write(buffer);
                buffer = 0;
                count = 0;
            }
        }

        public void close() throws IOException {
            if (count > 0) {
                buffer <<= (8 - count);
                out.write(buffer);
            }
            out.close();
        }
    }

    private static class BitInputStream {
        private InputStream in;
        private int buffer;
        private int count;

        public BitInputStream(InputStream in) {
            this.in = in;
            buffer = 0;
            count = 0;
        }

        public int readBit() throws IOException {
            if (count == 0) {
                buffer = in.read();
                if (buffer < 0) return -1;
                count = 8;
            }
            int bit = (buffer >> (count - 1)) & 1;
            count--;
            return bit;
        }

        public void close() throws IOException {
            in.close();
        }
    }
}

Main.java

import java.io.IOException;

public class Main {
    public static void main(String[] args) throws IOException, ClassNotFoundException {
        HuffmanTree huffmanTree = new HuffmanTree();
        huffmanTree.initialize();
        huffmanTree.encoding();
        huffmanTree.decoding();
        huffmanTree.printingCodeFile();
        huffmanTree.printingHuffmanTree();
    }
}

测试数据：

输入：

26
A 186
B 64
C 13
D 22
E 32
F 103
G 21
H 15
I 47
J 57
K 1
L 5
M 32
N 57
O 63
P 15
Q 1
R 48
S 51
T 80
U 23
V 8
W 18
X 1
Y 16

输出：

CodePrin：

0000000000000000000000000000000000000000001001000000000011110101000000000001000000000011010000010001010000000000010001000000000000000000100000110100110001000000000000100000000000000000000010010010
01000000000000000100000000000000000000000000000000001001000000000001000101010000000100000000000000000000000101100001000001000000010000000000000000000000000000000001000000000010100000000000110100
0000000000000000000000000000000000000000000000000000000000100000000000000000000000000000000000000100000000001010000000000000000010100000000000000000000000000000000000000000000000000000000000000
0000100100000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

TextFile：

THIS PROGRAM IS MY FAVORITE

TreePrint：

-
  |
  A
  |
  -
    |
    -
      |
      B
      |
      -
        |
        C
        |
        -
          |
          D
          |
          -
            |
            E
            |
            -
              -
                |
                G
                |
                -
              -
                |
                H
                |
                -
            -
              |
              I
              |
              -
                -
                  |
                  J
                  |
                  -
                -
                  |
                  -
                    |
                    M
                    |
                    -
            -
              |
              -
                |
                N
                |
                -
                  |
                  O
                  |
                  -
                    |
                    P
                    |
                    -
            -
              |
              -
                |
                Q
                |
                -
          -
            |
            R
            |
            -
              |
              S
              |
              -
                |
                T
                |
                -
                  |
                  -
                    |
                    V
                    |
                    -
                  -
                    |
                    W
                    |
                    -
                      |
                      X
                      |
                      -
                -
                  |
                  Y
                  |
                  -