java - XSSF。空指针异常

Question

private void cleaner(Integer columnsCount, Integer rowsCount, Object object){
    int firstColumn=0;
    int firstRow=0;
    XSSFSheet sheet = workBook.getSheetAt(0);
    for (int lineId=firstRow;lineId<rowsCount;lineId++)   {
        XSSFRow row = sheet.getRow(lineId);
        for (int columnId=firstColumn;columnId<columnsCount;columnId++){
            row.createCell(columnId).setCellValue(object.toString());  }
    }
}

我真的不明白这个逻辑。首先，我得到行，然后尝试写入数据。我当然知道，我的所有数据都不为空。 但编译器说:

Exception in thread "main" java.lang.NullPointerException
    at workhere.WriterXlsx.cleaner(WriterXlsx.java:75)
    at workhere.WriterXlsx.<init>(WriterXlsx.java:19)
    at workhere.Start.main(Start.java:28)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:120)

WriterXlsx.java:75 : row.createCell(columnId).setCellValue(object.toString());

我用以下代码开始此方法:cleaner(30,30,"");

Answer 1

看看API

sheet.getRow(lineId);

如果行不存在则返回 null。您需要create在访问该行之前先添加一行，以防该行不存在(或跳过它)。