POI：make fields static FindBugs warning: ExcelStyleDateFormatter doesn't override java.text.SimpleDAtaFormat.equals(Object) add hashCode for corresponding equals function
POI：make fields static
FindBugs warning: ExcelStyleDateFormatter doesn't override java.text.SimpleDAtaFormat.equals(Object)
add hashCode for corresponding equals function

tonyqus/npoi,antony-liu/npoi