Write items into excel cell

I am absolute new to the Eclipse Java coding. I am trying to finish a project for managing the inventory. The part i am having trouble with is that, when I tried to write the items into the excel cell, I got errors saying that the array is out of bounds.

PS: item and item.getPartname etc are all defined under another class file. Please help. thanks

            FileOutputStream os =new FileOutputStream("orderreceipt");
            //Create a new workbook for writing data
            HSSFWorkbook wb2 = new HSSFWorkbook();
            //Create a new sheet:
            HSSFSheet newsheet = wb2.createSheet("MyNewSheet");
            //Create a new row:

            for (int i=0; i<6; i++){
                HSSFRow newrow = newsheet.createRow(i);
                sentorder item = (sentorder)items.get(i);
                for (short j=0; j<5; j++){
                    HSSFCell cell = newrow.createCell(j);

                    cell.setCellValue(item.getPartname());
                    cell.setCellValue(item.getPartnumber());
                    cell.setCellValue(item.getQuantity());
                    cell.setCellValue(new Date());
                      HSSFCellStyle styleOfCell = wb2.createCellStyle();
                      styleOfCell.setDataFormat(HSSFDataFormat
                          .getBuiltinFormat("m/d/yy"));
                      styleOfCell.setFillForegroundColor(HSSFColor.AQUA.index);
                      styleOfCell.setFillPattern(HSSFCellStyle.BORDER_THIN);
                      cell.setCellStyle(styleOfCell);

                    }}
            wb2.write(os);
    }

I can see quite a few problems with the attached code:

Missing file extension when creating new FileOutputStream - since you're generating the .xls workbook, you'd probably like to store it in the XLS file (the extension is not added automatically), also just make sure you have a proper file path to the directory you have write permissions (local application dir, as in this case should be ok though).
As already mentioned you are re-setting the same cell value 4 times
You are creating the same cell style multiple times (this is not cached behind the scenes and there is largely limited number of cells styles which can be created so if you were generating a couple thousands of rows you might get into troubles
You don't flush() and close() stream after writing your workbook. Streams in Java a precious resources which need to be manually closed.
Without stack trace it's difficult to say 100% where the ArrayOutOfBound issue you're seeing is coming from, however my guess would be that you're trying to access a item (from items collection) with the index that doesn't exist, which is a consequence that you're driving your report data from row indexes instead of the list of items you have.

Also, since you're quite new to Java a couple of guidelines which will allow you to produce hopefully better and less error-prone code in the future:

Use proper Java naming convention - please follow standard Java naming convention http://java.about.com/od/javasyntax/a/nameconventions.htm , your code will be easier to read and reason about (especially when you're looking for help from community) - i.e. sentorder class should be named as SentOrder.
Try to split your code into smaller, more testable modules i.e. you can have a helper createDataRow method called from your main method, in general having more than a couple of inner loops in one method makes them incredibly difficult to test, debug and reason about.
Unless you really need to generate .xls format, consider using XSSF* classes for generating xlsx document - it has many improvements over HSSF* (including much better dataFormat support).

Having those in mind I've rewritten your example:

public void improved(List<SentOrder> items) throws IOException {
    HSSFWorkbook workbook = new HSSFWorkbook();
    HSSFSheet sheet = workbook.createSheet("MyNewSheet");

    HSSFCellStyle styleOfCell = workbook.createCellStyle();
    styleOfCell.setDataFormat(HSSFDataFormat.getBuiltinFormat("m/d/yy"));
    styleOfCell.setFillForegroundColor(HSSFColor.AQUA.index);
    styleOfCell.setFillPattern(HSSFCellStyle.BORDER_THIN);

    int rowIndex = 0;
    for(SentOrder item : items) {
        HSSFRow row = sheet.createRow(rowIndex++);
        HSSFCell nameCell = row.createCell(0);
        nameCell.setCellValue(item.getPartName());
        HSSFCell numberCell = row.createCell(1);
        numberCell.setCellValue(item.getPartNumber());
        HSSFCell quantityCell = row.createCell(2);
        quantityCell.setCellValue(item.getQuantity());
        HSSFCell dateCell = row.createCell(3);
        dateCell.setCellValue(new Date());
        dateCell.setCellStyle(styleOfCell);
    }

    FileOutputStream os = new FileOutputStream("order_receipt.xls");
    try {            
        workbook.write(os);
    } finally {
        os.flush();
        os.close();
    }
}