How to get the formula cell value(data) using apac

I am using Apache poi-3.1-FINAL-20080629 in my application. here, I have one problem using formula...

My Cell has formula(sheet2!C10) and the data inside this cell is String type (e.g $3,456)...How to access that cell also want to display the formula.

My code Looks like:

HSSFWorkbook wb = new HSSFWorkbook(file);
HSSFSheet sheet = wb.getSheetAt(0);
HSSFFormulaEvaluator evaluator = new HSSFFormulaEvaluator(sheet, wb);

Iterator rows = sheet.rowIterator();
    while (rows.hasNext()) {
        HSSFRow row = (HSSFRow) rows.next();
        System.out.println("\n");
        Iterator cells = row.cellIterator();
        while (cells.hasNext()) {

            HSSFCell cell = (HSSFCell) cells.next();

            int cellType = cell.getCellType();

            if (HSSFCell.CELL_TYPE_NUMERIC == cellType)
                System.out.print(cell.getNumericCellValue() + "     ");
            else if (HSSFCell.CELL_TYPE_STRING == cellType)
                System.out.print(cell.getStringCellValue() + "     ");
            else if (HSSFCell.CELL_TYPE_BOOLEAN == cellType)
                System.out.print(cell.getBooleanCellValue() + "     ");
            else if (HSSFCell.CELL_TYPE_BLANK == cellType)
                System.out.print("BLANK     ");
            else if (HSSFCell.CELL_TYPE_FORMULA == cellType) {
                System.out.print(evaluator.evaluateInCell(cell).toString()  );              }   else 
                System.out.print("Unknown cell type " + cellType);

        }

    }

evaluator.evaluateInCell(cell).toString() is throwing null pointer exception. Please Help!!!

OK, so first up, Apache POI 3.1 is rather old. The clue is in the jar name - poi-3.1-FINAL-20080629 dates from 2008, so 6 years ago! It's well worth upgrading, the number of bug fixes since then is pretty vast....

As for your problem, I'm fairly sure that you don't want to be calling evaluator.evaluateInCell. That's almost never the right method to call

You have three options available to you, depending on what you want to do with your formula cell:

I want the formula string

Call Cell.getCellFormula and you'll get back the formula string

I want the last formula value Excel calculated

When Excel writes out a file, it normally stores the last evaluated value for the formula, in a cache, to make opening nice and quick. You can read this, if present, from Apache POI. It's only a cache, so it might not always be correct, but it normally is.

You need to call Cell.getCachedFormulaResultType, then switch on that, and read the values out using the normal getters, eg

int cellType = cell.getCellType();
handleCell(cell, cellType);

private void handleCell(Cell cell, int cellType) {
        if (HSSFCell.CELL_TYPE_NUMERIC == cellType)
            System.out.print(cell.getNumericCellValue() + "     ");
        else if (HSSFCell.CELL_TYPE_STRING == cellType)
            System.out.print(cell.getStringCellValue() + "     ");
        else if (HSSFCell.CELL_TYPE_BOOLEAN == cellType)
            System.out.print(cell.getBooleanCellValue() + "     ");
        else if (HSSFCell.CELL_TYPE_BLANK == cellType)
            System.out.print("BLANK     ");
        else if (HSSFCell.CELL_TYPE_FORMULA == cellType)
            handleCell(cell, cell.getCachedFormulaResultType());
        else 
            System.out.print("Unknown cell type " + cellType);
   }

I want Apache POI to calculate the formula result for me

Your best bet here is to get a FormulaEvaluator object and call evaluate:

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;
}

The Apache POI Formula Evaluation page has more on all of these