Test.java

public class Test {
   public static void main(String[] args) {
      byte first = 0x0F;
      byte second = 0x0B;
      byte concat = 0x00;

      System.out.printf("Before, first=%s, second=%s, concat=%s.\n",
         printBinary(first),
         printBinary(second),
         printBinary(concat));

      concat = (byte) (((byte) (first <<  4)) | second);

      System.out.printf("After, first=%s, second=%s, concat=%s.\n",
         printBinary(first),
         printBinary(second),
         printBinary(concat));
   }

   public static String printBinary(byte binaryNumber){
      StringBuilder b = new StringBuilder(8);

      int binary = 0 | binaryNumber;
      int bitCount = 8;

      for(int i = 0; i < bitCount; i++){
         int j = 1 << bitCount - 1 - i;
         if( (binary & j) != 0 ){
            b.append('1');
         } else {
            b.append('0');
         }

      }
      return b.toString();
   }
}