You have a couple of things wrong here. First, getArrayLengths returns an array of dimensions. Second, you actually want to ‘mux’ your array, instead fo ‘demux’.

  /**
   * Multiplex multi-dimension array (x[][][]) to single-dimension array (x[]).
   *
   * @param src multi-dimension array
   * @param dims an array of int.
   * @return single-dimension array
   */
  public static Object muxArray(Object src, int[] dims)

  /**
   * Demux single-dimension array (x[]) to a multi-dimension array (x[][][]).
   *
   * @param src single-dimension array
   * @param dims an array of int.
   * @return multi-dimension array
   */
  public static Object demuxArray(Object src, int[] dims)

So, try this:

  @Test
  public void testDemuxArray2() {
    int src[][] = new int[][] {{1, 2, 3}, {2, 3, 4}};
    int[] dims = MultiDimensionArrayUtils.getArrayLengths(src);
    MultiDimensionArrayUtils.muxArray(src, dims);
  }

But – what are you actually trying to do? If you just wish to deliver arrays via OPC UA variables, you don’t need to multiplex them yourself – the SDK will do this automatically for you.

PS. ‘<pre>’-tags help with keeping the outline of code.

Usually you don’t need to use it yourself, since the SDK uses it internally, whenever needed.

That’s why I asked that what are you actually trying to do?

Yes, you don’t need to that yourself, and you can expect that you always receive the multidimensional arrays demuxed for you.

Yes the OPC UA Stack uses the mix and demux internally. But if your server puts a three dimensional array in a Variant, it comes out as a three dimensional array in a Variant in the client.

So the mixing is just used to transfer data over wire in OPC UA, but when you use the SDK and Stack, you don’t need to care about that.