java - 尝试将结果写入 Excel 时出现 NullPointerException

Question

有人可以帮忙处理这段代码吗？
我在第 41 行收到有关 NullPointerException 的错误消息。我知道它返回 null，但以下验证需要该值。一般任务是将结果写入excel文件。

 public class ExcelUtils {

        public static void main(String[] args)
        {
            //Blank workbook
            XSSFWorkbook workbook = new XSSFWorkbook();

            //Create a blank sheet
            XSSFSheet sheet = workbook.createSheet("Employee Data");

            String Result = "TEST TEST TEST";
            int RowNum = 2;
            int ColNum = 3;
            XSSFSheet ExcelWSheet = sheet;
            XSSFCell Cell;
            XSSFRow Row;

            try
                {


                    Row  = ExcelWSheet.getRow(RowNum);

                    Cell = Row.getCell(ColNum, org.apache.poi.ss.usermodel.Row.RETURN_BLANK_AS_NULL);

                    if (Cell == null) {

                        Cell = Row.createCell(ColNum);

                        Cell.setCellValue(Result);

                        } else {

                            Cell.setCellValue(Result);

                        }




                //---------------------------------------------------


                    //try
                   // {
                    //Write the workbook in file system
                    FileOutputStream out = new FileOutputStream(new File("howtodoinjava_demo.xlsx"));
                    workbook.write(out);
                    out.close();
                    System.out.println("howtodoinjava_demo.xlsx written successfully on disk.");
                }
                catch (Exception e)
                {
                    e.printStackTrace();
                }

        }


    }

Answer 1

将结果字符串从测试方法传递到方法 writeexcel。您不需要创建对象，因为该方法是静态的

writeexcel("pass",2,3);

这将调用 writeexcel 方法，并将作为参数传递的字符串写入相应的单元格中，即“pass”

方法:

public static void writeexcel(String Result,int RowNum ,int ColNum)
    {
        //Blank workbook
        XSSFWorkbook workbook = new XSSFWorkbook();

        //Create a blank sheet
        XSSFSheet sheet = workbook.createSheet("Employee Data");
        XSSFSheet ExcelWSheet = sheet;
        XSSFCell Cell;
        XSSFRow Row;

        try
            {


                Row  = ExcelWSheet.createRow(RowNum);

                Cell = Row.getCell(ColNum, org.apache.poi.ss.usermodel.Row.RETURN_BLANK_AS_NULL);

                if (Cell == null) {

                    Cell = Row.createCell(ColNum);

                    Cell.setCellValue(Result);

                    } else {

                        Cell.setCellValue(Result);

                    }

                FileOutputStream out = new FileOutputStream(new File("howtodoinjava_demo.xlsx"));
                workbook.write(out);
                out.close();
                System.out.println("howtodoinjava_demo.xlsx written successfully on disk.");
            }
            catch (Exception e)
            {
                e.printStackTrace();
            }

    }

编辑

public class Tests {

    static XSSFWorkbook workbook = new XSSFWorkbook();

    static  XSSFSheet sheet = workbook.createSheet("Employee Data");

    public static void main(String[] args) {

        int j=3;

    for(int i=2;i<=5;i++) { 

        String result = "Test "+i;

        writeexcel(result, i, j);

    }
    writetoexcel();//write to cell(2,3),(3,3),(4,3)
    }

    public static void writeexcel(String Result,int RowNum ,int ColNum)
    {

        //Create a blank sheet

        XSSFSheet ExcelWSheet = sheet;
        XSSFCell Cell;
        XSSFRow Row;

        try
            {
                Row  = ExcelWSheet.createRow(RowNum);

                Cell = Row.getCell(ColNum, org.apache.poi.ss.usermodel.Row.RETURN_BLANK_AS_NULL);

                if (Cell == null) {

                    Cell = Row.createCell(ColNum);

                    Cell.setCellValue(Result);

                    } else {

                        Cell.setCellValue(Result);

                    }

            }
            catch (Exception e)
            {
                e.printStackTrace();
            }
    }

    public static void writetoexcel(){

        try{
            FileOutputStream out = new FileOutputStream(new File("howtodoinjava_demo.xlsx"));
            workbook.write(out);
            out.close();
            System.out.println("howtodoinjava_demo.xlsx written successfully on disk.");
            }catch (Exception e)
            {
                e.printStackTrace();
            }

    }
    }

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