code: public static byte[] append(byte[] a, byte[] b) {
          byte[] z = new byte[a.length + b.length];
          System.arraycopy(a, 0, z, 0, a.length);
          System.arraycopy(b, 0, z, a.length, b.length);
          return z;
      }
docs: Appends two bytes array into one.
  
  @param a A byte[].
  @param b A byte[].
  @return A byte[].