code: public static <T> T[] concat(T[] first, T[] second) {
          T[] result = Arrays.copyOf(first, first.length + second.length);
          System.arraycopy(second, 0, result, first.length, second.length);
          return result;
      }
docs: concat 2 array to a new array.
  
  @param first  first array, can not be null
  @param second second array, can not be null
  @return the result array.
  @deprecated This method can not cocat null object and only supports concating of 2 arrays. Use {@link #concatV2(Class, Object[][])} instead.