class DataProvider {

    public void setPageSize(int pageSize) {
        int oldPageSize = pageInfo.getPageSize();
        pageInfo.setPageSize(pageSize);
        if (oldPageSize != pageInfo.getPageSize()) {
            applyFilterSortAndPaging();
            showItems();
            updateSelection();
        }
    }

    public  DataProvider(Function<T, String> identifier, boolean multiSelect);
      DataProvider(Function<T, String> identifier, boolean multiSelect, int pageSize);

}