Question

I write the bitstream for a JPEG Encoder, I’m facing this problem:

I built Pairs for the AC Cosinus Coefficients (after Quantization) in an int[]array. Each Pair: (Number of Zeros/ Category of the Coefficient after JPEG standard). Out of these two integers, I have to form one hexadecimal number, where as one integer of the pair representing one nibble. The hexadecimal Numbers have to be huffman-encoded later.
Example: My Pair is (4,5), i need it as (0x45).

How can I do that? My way is to convert the Integers to a String, append the Strings, and get them back as one Integer. However, the compiler says

Exception in thread “main” java.lang.NumberFormatException: For input string: “0fffffff5”

//Get a Pair (Numbers of Zeros, Coefficient)
            int[]singlePair_ref = acPairs_ref.get(i);

            //Convert to Wrapper Class Integer
            Integer firstNibble_ref = ((Integer)singlePair_ref[0]);
            Integer secondNibble_ref = ((Integer)singlePair_ref[1]);

            //Convert to String
            String firstNibbleString_ref = firstNibble_ref.toHexString(singlePair_ref[0]);
            String secondNibbleString_ref = secondNibble_ref.toHexString(singlePair_ref[1]);

            //Append Strings
            String byteValueString_ref = firstNibbleString_ref+secondNibbleString_ref;
            Integer byteValue_ref = 0;

            //Convert the new formed "one" (formed out of two) Number back to Integer
            byteValue_ref.parseInt(byteValueString_ref); //Line throws Exception

Hope you can help me. Thanks a lot!
Daniel

Edit:
if I do it like this

YACforHuffman_ref[i] = (singlePair_ref[0] << 4) | singlePair_ref[1];

the out put is decimal (3,6) becomes 54. If I convert the result of this equation with

String YACforHuffman_ref = Integer. Integer.toHexString((singlePair_ref[0] << 4) |    singlePair_ref[1];

like Mike did above, I get trouble for a value bigger than 9 (Value A-F), now I know what you meant @Mike, sorry I didnt get it at first. How can I solve this?

Answer 1

I’m unsure how you would pass in values over 9 into your integer pair but assuming you can pass in 0-15 then you could potentially do something such as this:

public class Hex {
    public static void main(String[] args) {
        int firstNum  = 4;
        int secondNum = 15;

        System.out.println( Integer.toHexString( firstNum * 16 + secondNum ) );
        // Or if you find it easier to understand
        // System.out.println( Integer.toHexString( ( firstNum << 4 ) + secondNum ) );
    }
}