code: private void addColumnSelectExample() {
  		add(new WHeading(HeadingLevel.H3, "WCheckBoxSelect laid out in columns"));
  		add(new ExplanatoryText("Setting the layout to COLUMN will make the check boxes be rendered in 'n' columns. The number of columns is"
  				+ " determined by the layoutColumnCount property."));
  		final WCheckBoxSelect select = new WCheckBoxSelect("australian_state");
  		select.setToolTip("Make a selection");
  		select.setButtonLayout(WCheckBoxSelect.LAYOUT_COLUMNS);
  		select.setButtonColumns(2);
  		add(select);
  
  		add(new WHeading(HeadingLevel.H3, "Options equal to columns"));
  		String[] options = new String[]{"Dog", "Cat", "Bird"};
  		final WCheckBoxSelect select2 = new WCheckBoxSelect(options);
  		select2.setToolTip("Animals");
  		select2.setButtonColumns(3);
  		final WTextField text = new WTextField();
  		text.setReadOnly(true);
  		text.setText(NO_SELECTION);
  
  		WButton update = new WButton("Select Animals");
  		update.setAction(new Action() {
  			@Override
  			public void execute(final ActionEvent event) {
  				String output = select2.getSelected().isEmpty() ? NO_SELECTION : "The selected animals are: "
  						+ select2.getSelected();
  				text.setText(output);
  			}
  		});
  		select2.setDefaultSubmitButton(update);
  
  		add(select2);
  		add(update);
  		add(text);
  		add(new WAjaxControl(update, text));
  	}
docs: adds a WCheckBoxSelect with LAYOUT_COLUMN in 2 columns.