当每个字符的位数变化时，如何从BitInputStream中读取每个字符

Question

I apologize, it wouldn't let me tag homework.

Hello there, I'm working on a school project using Huffman coding to compress data from a file. In this assignment, you are supposed to read from a file using a BitInputStream object, which I'm not sure is in the JCL because the documentation the professor provided has spelling errors and isn't very explicit with certain things. Anyway, it seems to work about the same as other classes that extend InputStream. The lines of code I keep getting from the class forum are the following:

        try {
            BitInputStream b = new BitInputStream(in);
            int data;

            while((data  = b.readBits(BITS_PER_WORD)) != -1) {
                data = b.readBits(BITS_PER_WORD);
                q.freq[data]++; //instance variable (size 256) in PriorityQueue q to 
                //count number of occurrences of each piece of data.
                System.out.println(data);
            }
        }catch(FileNotFoundException e) {
            System.out.println("File not found.");
        }
        catch(IOException e) {
            System.out.println("Error while reading file.");
        }

...where @param in is the generic input stream object and BITS_PER_WORD = 8, inherited from an interface of constants. The problem is that whenever I run this, it appears to skip every other character in the file, starting with the first. So, for example, the small .txt file containing "Eerie eyes seen near lake." would print: 101 105 32 121 115 115 101 32 101 114 108 107 46 10 ('e', 'i', ' ', 'y', etc..). I imagine this has something to do with trying to read 8 bits at a time, as the ascii value of 'a' for example, in bits, is 1100001 (7 bits) and space is 100000 (6 bits). I was wondering if I have to somehow vary the number of bits it's trying to read (and how on earth I would do that) or if I'm coming at this the wrong way (I've only recently gotten used to the idea of working with bits/bytes and there may be something important I don't know).

I apologize for the lengthy question, but let me know if I left out any important info. Thanks!

Answer 1

You seem to be calling readBits() an extra time in the while initialisation. This might be why it is skipping letters. You should have something like:

while(data != -1) {
  data = b.readBits(BITS_PER_WORD);