您好我正在编写一个关于编写我们自己的霍夫曼编码的项目。我目前在将二进制1和0写入输出文件时遇到问题。它适用于较小的输入文件，但对于非常大的文件，它不会向输出文件写入任何内容。负责编写的方法是compress方法。任何帮助，将不胜感激。谢谢！
package proj3;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Scanner;
import java.util.PriorityQueue;
public class Project3 {
//variables for PriorityQueue and Huffman Tree
private static PriorityQueue<BinaryNode<Character>> queue;
private static BinaryNode<Character> huffTree;
private static Map<Character, String> table = new LinkedHashMap<Character, String>();
/**
* Method for creating Huffman Tree
* @param counts Map that contains all characters and their frequencies
* @return the Huffman Tree
*/
public static BinaryNode<Character> makeTree(Map<Character, Integer> counts)
{
queue = new PriorityQueue<BinaryNode<Character>>();
for(Character c : counts.keySet())
{
BinaryNode<Character> tree = new BinaryNode<Character>(c, counts.get(c), null, null);
queue.add(tree);
}
while(!queue.isEmpty())
{
if(queue.size() >= 2)
{
BinaryNode<Character> n1 = queue.remove();
BinaryNode<Character> n2 = queue.remove();
Integer weight = n1.getFreq() + n2.getFreq();
huffTree = new BinaryNode<Character>(null, weight, n1, n2);
queue.add(huffTree);
}
if(queue.size() == 1)
{
return queue.remove();
}
}
return huffTree;
}
public static void encode(BinaryNode<Character> node, String s)
{
if(!node.isLeaf())
{
encode(node.getLeft(), s + "0");
encode(node.getRight(), s + "1");
}
else
{
table.put(node.getElement(), s);
}
}
public static void compress(String in, String out) throws IOException
{
try
{
File outFile = new File(out);
FileOutputStream compressedFile = new FileOutputStream(outFile);
Scanner infile = new Scanner(new FileInputStream(in));
while(infile.hasNext())
{
infile.useDelimiter("");
String str = infile.next();
Character character = str.charAt(0);
for(Character c : table.keySet())
{
if(c == character){
compressedFile.write(table.get(c).getBytes());
compressedFile.flush();
}
}
}
for(Byte b : table.get('^').getBytes())
{
compressedFile.write(b);
}
infile.close();
compressedFile.close();
}
catch (FileNotFoundException e)
{
System.err.println("File not found.");
e.printStackTrace();
}
}
public static void decompress(String s)
{
}
public static void printEncodings(Map<Character, String> m)
{
ArrayList<Character> chars = new ArrayList<Character>();
System.out.println("Character Encodings");
System.out.println("---------------------");
for(Character c : m.keySet())
{
chars.add(c);
Collections.sort(chars);
}
for(Character c : chars)
{
System.out.print(c + "\t" + m.get(c) + "\n");
}
System.out.println();
System.out.println("Total Characters: " + chars.size());
}
/**
* Method for creating map with character and its frequencies
* @param s the file name to be opened
* @return the Map containing characters and frequencies
*/
public static Map<Character, Integer> charCount(String s){
Map<Character, Integer> counts = new LinkedHashMap<Character, Integer>();
ArrayList<Character> chars = new ArrayList<Character>();
try {
Scanner file = new Scanner(new FileInputStream(s));
while(file.hasNext()){
file.useDelimiter("");
String str = file.next();
Character c = str.charAt(0);
if(counts.containsKey(c)){
counts.put(c, counts.get(c) + 1);
}
else{
counts.put(c, 1);
}
}
counts.put('^', 1);
System.out.println("Character Frequencies");
System.out.println("---------------------");
for(Character c : counts.keySet())
{
chars.add(c);
Collections.sort(chars);
}
for(Character c : chars){
System.out.println(c + "\t" + counts.get(c));
}
System.out.println();
System.out.println("Total characters: " + chars.size() + "\n");
file.close();
}
catch (FileNotFoundException e) {
System.err.println("File not found.");
System.exit(0);
}
return counts;
}
public static void main(String[] args){
if(args.length != 3)
{
throw new IllegalArgumentException("Invalid number of arguments.");
}
encode(makeTree(charCount(args[0])), "");
printEncodings(table);
try {
compress(args[0], args[1]);
} catch (IOException e) {
e.printStackTrace();
}
}
}
答案 0 :(得分：0)
您可能需要致电compressedFile.flush()
像这样改进
if(c == character){
compressedFile.write(table.get(c).getBytes());
compressedFile.flush();
}
另外考虑使用try/catch。将提高实施的完整性。
答案 1 :(得分：0)
我很确定你在compress（）方法中遇到了性能/内存问题。编码在主方法中打印正常，但我相信文件输出会卡住。我可以在代码中看到至少三种优化的可能性：
您正在使用Scanner来按字符串读取输入文件char，但您不使用Scanner提供的任何解析功能。请尝试改为使用InputStreamReader。
您正在循环Huffman表中的一组键并检查是否相等。您可以简单地使用当前char来获取它映射到的String并省略循环。
您无需循环字节数组以将其写入输出文件。 FileOutputStream的write（）方法可以将整个字节数组作为参数。
凭借我谦逊的Java技能，我宁愿以下面的方式实现它;请注意，这是未经测试的代码，因为我没有您的BinaryNode类：
public static void compress(String in, String out) throws IOException
{
try
{
File outFile = new File(out);
FileOutputStream compressedFile = new FileOutputStream(outFile);
// 1. Use a Reader instead of a Scanner;
// make sure to use the correct charset
FileInputStream fis= new FileInputStream(in);
Reader reader = new InputStreamReader(fis,
Charset.forName("US-ASCII"));
// use BufferedReader for even better performance
Reader bufferedReader = new BufferedReader(reader);
int r;
while ((r = bufferedReader.read()) != -1) {
char ch= (char) r;
// 2. Get the string for this character directly instead of
// looping the keySet and checking for equivalence
String s= table.get(ch);
if (s != null) {
// 3. Write entire array of bytes instead of
// looping and writing bytes one by one
compressedFile.write(s.getBytes());
}
}
fis.close();
compressedFile.close();
}
...