code: @Override
      public void setParam(String key, INDArray val) {
          //Set params for MultiLayerNetwork sub layers.
          int idx = key.indexOf('_');
          if (idx == -1)
              throw new IllegalStateException("Invalid param key: not have layer separator: \"" + key + "\"");
          int layerIdx = Integer.parseInt(key.substring(0, idx));
          String newKey = key.substring(idx + 1);
  
          layers[layerIdx].setParam(newKey, val);
      }
docs: Set the values of a single parameter. See {@link #setParamTable(Map)} and {@link #getParam(String)} for more
  details.
  @param key the key of the parameter to set
  @param val the new values for the parameter