My mask doesn't work for reading bits

Question

the following table represents a stream of bits. within the bits are certain fields that i need to be able to read, and extract. I tried writing code to do pretty much exactly what I need, but the mask isn't working. here is the exact situation of what I have:
| 15 | 14 | 13| 12| 11| 10| 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
|-----------------Word Count--------------------------------------| word 1
| 0- | 1-- |-------------Message_ID------|----unused---------| word 2
|---------------------stuff I don't care about here -------------| word 3
| --------------- more stuff I don't care about here ---------| word 4
My goal in writing this code was to extract the Message_ID and put it in its own file. to do that I wrote code to skip the first word (which is two bytes) and read the second word after shifting the Message_ID to the far right (at least thats what I thought the coding would do :) Again, thank you for all your guys' help
well here is the short java file that I wrote, its not long so please look at it and tell me why it wont mask and shift the Message_ID and write it into a new file
import java.io.*;
public class Mask {
public static void main(String[] arguments) {
try {
// create object to be read
File bits = new File("c:/test.txt");
FileInputStream file = new FileInputStream(bits);
//skip the first two bytes
file.skip(2);
//read the next two bytes
byte[] ary = new byte[2];
//read file that contains bits
file.read(ary);
//create a mask
int i = 0;
int messageIDBits = (i >> 6) & 0xFF;
//create object to write the bits which were read
File txt = new File("c:/test1.txt");
FileOutputStream messageID = new FileOutputStream(txt);
//write the bits containing the Message_ID
messageID.write(ary);
//close the files
file.close();
messageID.close();
} catch (Exception e) {
System.out.println("Error -- " + e.toString());
}

Answer 1

Sorry it took so long - had a meeting. Here's the demo. Run it, study it, and let me know if you have any questions:import java.io.*;
import java.util.*;
class BytesDemo {
    private static Random rand = new Random();
    public static void main(String[] args) {
        new BytesDemo().go();
    void go() {
        byte[] testBytes = new byte[2];
        rand.nextBytes(testBytes);
        System.out.println("Here are our starting bytes (" +
                            testBytes[0] + ", " +
                            testBytes[1] + "):");
        System.out.println(toBinary(testBytes[0], 8) +
                         " " +
                         toBinary(testBytes[1], 8));
        System.out.println("\nNow, we'll call the getMessageId() method...");
        int messageId = getMessageId(testBytes);
        System.out.println("\nOur final message ID is: \n" + messageId);
        System.out.println("\nAnd here's the short version: " + getId(testBytes));
    int getMessageId(byte[] b) {
        if (b.length != 2) throw new IllegalArgumentException("I need two bytes!");
        System.out.println("\nFirst, we'll create the word.");
        System.out.println("Here is the first byte, shifted to the left: \n" +
                           toBinary(b[0] << 8, 16));
        System.out.println("\nHere is the second byte, kept as it is: \n" +
                           toBinary(b[1] & 0xFF, 16));
        System.out.println("\nNow we will OR the two together...");
        int word = (b[0] << 8) | (b[1] & 0xFF);
        System.out.println("...resulting in the word: \n" + toBinary(word, 16));
        System.out.println("\nThe first 6 bits aren't needed, so we'll shift the word:");
        word = word >> 6;
        System.out.println(toBinary(word, 16));
        int mask = 0xFF;
        System.out.println("\nOur mask looks like this: \n" + toBinary(mask, 16));
        System.out.println("\nSo now, we'll AND the shifted word and the mask together...");
        int messageId = word & mask;
        System.out.println(toBinary(messageId, 8));
        return messageId;
    int getId(byte[] b) {
        if (b.length != 2) throw new IllegalArgumentException("I need two bytes!");
        int word = (b[0] << 8) | (b[1] & 0xFF);
        return (word >> 6) & 0xFF;
    String toBinary(int num, int bits) {
        StringBuffer buf = new StringBuffer(Integer.toBinaryString(num));
        int len = buf.length();
        if (len > bits) buf.delete(0, len - bits);
        while (len++ < bits) {
            buf.insert(0, "0");
        return buf.toString();
}