code: public void setButtonColumns(final int numColumns) {
  		if (numColumns < 1) {
  			throw new IllegalArgumentException("Must have one or more columns");
  		}
  
  		CheckBoxSelectModel model = getOrCreateComponentModel();
  		model.numColumns = numColumns;
  		model.layout = numColumns == 1 ? LAYOUT_STACKED : LAYOUT_COLUMNS;
  	}
docs: Sets the layout to be a certain number of columns.
  
  @param numColumns the number of columns.