Upgrading to POI 3.5, including converting existing HSSF Usermodel code to SS Usermodel (for XSSF and HSSF) Wherever possible, we have tried to ensure that you can use your existing POI code with POI 3.5 without requiring any changes. However, Java doesn't always make that easy, and unfortunately there are a few changes that may be required for some users. org.apache.poi.hssf.usermodel.HSSFFormula