code: public int layerSize(int layer) {
          if (layer < 0 || layer > layers.length) {
              throw new IllegalArgumentException("Invalid layer index: " + layer + ". Layer index must be between 0 and "
                      + (layers.length - 1) + " inclusive");
          }
          return layerSize(layers[layer].conf().getLayer().getLayerName());
      }
docs: Return the layer size (number of units) for the specified layer.
  Note that the meaning of the "layer size" can depend on the type of layer. For example:<br>
  - DenseLayer, OutputLayer, recurrent layers: number of units (nOut configuration option)<br>
  - ConvolutionLayer: the channels (number of channels)<br>
  - Subsampling layers, global pooling layers, etc: size of 0 is always returned<br>
  
  @param layer Index of the layer to get the size of. Must be in range 0 to nLayers-1 inclusive
  @return Size of the layer