Managing bit flags in an array of bytes

Question

In my program, I have a large array of bytes. Some arbitrarily long groups of bytes in this array act as groups of bit flags. I need to be able to retrieve and manipulate these bit flags. I read that the best way to do this is with bitwise operations; something I have never learned before. I wrote methods that seem to work, but because I have never done anything like this before, can someone check my work?
Here is an example program, where the only contents of the byte array is a single two-byte grouping of 16 bit flags:
public class test
    static byte[] bytes = new byte[2];
    static byte[] pow2 = {1, 2, 4, 8, 16, 32, 64, -128};
    static byte[] pow2i = {-2, -3, -5, -9, -17, -33, -65, 127};
    public static void main(String[] args) throws Exception
        writeBitFlag(0, 6, true);
        for (int i = 0; i < 16; i++)   
            System.out.println("Flag " + i + ": " + getBitFlag(0, i));
        System.out.println();
        writeBitFlag(0, 12, true);
        invertBitFlag(0, 0);
        invertBitFlag(0, 0); 
        invertBitFlag(0, 1);
        for (int i = 0; i < 16; i++)   
            System.out.println("Flag " + i + ": " + getBitFlag(0, i));  
    }//end main
    public static boolean getBitFlag(int startAddress, int flag)
        return (bytes[startAddress + flag / 8] & pow2[flag %= 8]) == pow2[flag];
    }//end getBitFlag
    public static void invertBitFlag(int startAddress, int flag)
        bytes[startAddress + flag / 8] ^= pow2[flag % 8];
    }//end invertBitFlag
    public static void writeBitFlag(int startAddress, int flag, boolean flagVal)
        if (flagVal)
            bytes[startAddress + flag / 8] |= pow2[flag % 8];
        else
            bytes[startAddress + flag / 8] &= pow2i[flag % 8];
    }//end writeBitFlag      
}//end class testDoes this look like the right way to do what I am trying to do?

Answer 1

You could try BitSet which provides these function for you.
public class test { 
    public static void main(String[] args) throws Exception {   
        byte[] bytes = new byte[2];
        writeBitFlag(bytes, 6, true);
        for (int i = 0; i < bytes.length*8; i++)   
            System.out.println("Flag " + i + ": " + getBitFlag(bytes, i));
        System.out.println();
        writeBitFlag(bytes, 12, true);
        invertBitFlag(bytes, 0);
        invertBitFlag(bytes, 0); 
        invertBitFlag(bytes, 1);
        for (int i = 0; i < bytes.length*8; i++)   
            System.out.println("Flag " + i + ": " + getBitFlag(bytes, i));  
    }//end main
    public static boolean getBitFlag(byte[] bytes, int flag) {
        return ((bytes[flag >> 3] >> flag) & 1) != 0;
    public static void invertBitFlag(byte[] bytes, int flag) {
        bytes[flag >> 3] ^= (1 << (flag & 7));
    public static void writeBitFlag(byte[] bytes, int flag, boolean flagVal) {
        if (flagVal)
            bytes[flag >> 3] |= (1 << (flag & 7));
        else
            bytes[flag >> 3] &= ~(1 << (flag & 7));
}//end class test