Convert hex value stored in string to byte format

I have a hexa value(Fa) in a string. 
To add up some hexa values, first you need to convert each one of them into byte.
This program is used to convert a hexa value stored in string to byte format

/**
 *
 * Program to convert  hex value stored in string to  byte format
 *
 */

public class HexConversion
{           
            public static void main(String[] args)
            {
                        byte v = 0;
                        String s = "Fa";                       
                        byte[] b = s.trim().getBytes();
                        System.out.println(b[0]);
                        byte A, B;                       
                        A = getHexaValue(b[0]);
                        B = getHexaValue(b[1]);

                        System.out.printf("%X", A);
                        System.out.println();
                        System.out.printf("%X", B);
                        System.out.println();
                        /*
                         * Binary of F = 1111 (4 bits)
                         * Binary of a = 1010 (4 bits)
                         * The binary equivalent of Fa is 11111010
                         * b[0] = 70  = F = 00001111
                         * b[1] = 65 = a = 00001010
                         * To get both bytes in a single byte, left shift first byte to 4 positions
                         * OR it with v
                         * Then OR the second byte with v
                         * You will get the result as FA in a single byte
                         */
                        A = (byte) (A << 4); //left shifts value in A to 4 positions
                        System.out.printf("%X", A);
                        System.out.println();
                        v = (byte) (v | A);
                        System.out.printf("%X", v);
                        System.out.println();
                        v = (byte) (v | B);
                        System.out.printf("%X", v);
                        System.out.println();
            }

            //Returns the hexa value of the corresponding byte.
               //Hexa value is 4 in size
            private static byte getHexaValue(byte b)
            {
                        byte val = 0;
                        switch (b)
                        {
                                    case 65://A
                                    case 97://a           
                                                val = 0x0A;
                                                break;
                                    case 66://B
                                    case 98://b
                                                val = 0x0B;
                                                break;
                                    case 67://C
                                    case 99://c                                               
                                                val = 0x0C;
                                                break;
                                    case 68://D
                                    case 100://d
                                                val = 0x0D;
                                                break;
                                    case 69://E
                                    case 101://e
                                                val = 0x0E;
                                                break;
                                    case 70://F
                                    case 102://f
                                                val = 0x0F;
                                                break;
                                               
                                    case 49://1
                                                val = 0x01;
                                                break;
                                    case 50://2
                                                val = 0x02;
                                                break;
                                    case 51://3
                                                val = 0x03;
                                                break;
                                    case 52://4
                                                val = 0x04;
                                                break;
                                    case 53://5
                                                val = 0x05;
                                                break;
                                    case 54://6
                                                val = 0x06;
                                                break;
                                    case 55://7
                                                val = 0x07;
                                                break;
                                    case 56://8
                                                val = 0x08;
                                                break;
                                    case 57://9
                                                val = 0x09;
                                                break;
                        }
                        return val;
            }
}