Created attachment 27925 [details] Date arithmetic use case Excel directly supports arithmetic operations on non-numeric textcells. A1='2012/01/02 A2=A1-1 will display A2 as '2012/01/01' This is not possible with POI, also the DATEVALUE() function is currently not offered. Attached is a testcase, which exemplifies the above use case.
Same applies to date or time constants as arguments of the VALUE function (VALUE("11:45"). They will give a #VALUE! error on evaluation. see org.apache.poi.ss.formula.functions.Value.convertTextToNumber(String) Missing implementations of specialized functions DATEVALUE and TIMEVALUE, which would offer a workaround for the VALUE function in case of date/time constants.
DATEVALUE function is in recent versions of POI (eg POI 5.0.0). TIMEVALUE is not implemented yet.
TIMEVALUE is in v5.1.0