Java Apache-POI nullpointer异常，有关在现有行中创建单元格

Question

In the following code, I get a java.lang.NullPointerException on the first row.createCell(0) .

When I remove the spreadSheet.getRow(i+1) and the if-block after it, then replace them with spreadSheet.createRow(i+1) it all works.

Sadly doing it that way deletes some existing data in my rows, so I would like to be able to stop this null exception. Can't seem to figure out what is causing it though:

• i is definitely defined
• row is defined or we would create a new row in the if-block
• the cell is newly made with createCell() and thus doesn't have to be defined beforehand

I'm not sure what else to try, I'm mostly perplexed by how it does work when I create a new row but doesn't when I grab an existing one.

    //Clone template
    System.out.println(workbook.getNameIndex("template"));
    spreadSheet = workbook.cloneSheet(workbook.getNameIndex("template")+1, infoString);

    //Apply data to cells
    for (int i = 0; i < chartData.getItemCount();i++) {
        row = spreadSheet.getRow(i+1);
        if (row == null) {
            spreadSheet.createRow(i+1);
        }

        row.createCell(0).setCellValue(i+1);
        row.createCell(1).setCellValue(chartData.getDataItem(i).getXValue());
        row.createCell(2).setCellValue(chartData.getDataItem(i).getYValue());   

    }

Answer 1

You didn't assign the result of createRow back to row . Change

spreadSheet.createRow(i+1);

to

row = spreadSheet.createRow(i+1);