使用poi读取电子表格公式，执行完毕后为什么存放公式的单元格会读出空值？

[qq_15330517]

Cell cell = row.getCell(cellReference.getCol()); 利用system.out.这行输出的cell为空，为什么呢？
Java代码 如下：
FileInputStream fis = new FileInputStream("c:/temp/test.xls");
Workbook wb = new HSSFWorkbook(fis); //or new XSSFWorkbook("c:/temp/test.xls")
Sheet sheet = wb.getSheetAt(0);
FormulaEvaluator evaluator = wb.getCreationHelper().createFormulaEvaluator();

// suppose your formula is in B3
CellReference cellReference = new CellReference("B3");
Row row = sheet.getRow(cellReference.getRow());
Cell cell = row.getCell(cellReference.getCol());

CellValue cellValue = evaluator.evaluate(cell);

switch (cellValue.getCellType()) {
case Cell.CELL_TYPE_BOOLEAN:
System.out.println(cellValue.getBooleanValue());
break;
case Cell.CELL_TYPE_NUMERIC:
System.out.println(cellValue.getNumberValue());
break;
case Cell.CELL_TYPE_STRING:
System.out.println(cellValue.getStringValue());
break;
case Cell.CELL_TYPE_BLANK:
break;
case Cell.CELL_TYPE_ERROR:
break;

// CELL_TYPE_FORMULA will never happen
case Cell.CELL_TYPE_FORMULA:
break;
}