CODEWITHSUNDEEP
javaapache-poi
Badari Kodegenahalli
Badari Kodegenahalli

Reputation: 35

Query on protected constructor

Sorry for the dumb question. Following is the code that I have written to read from a spreadsheet using Apache POI. The line that I am confused is 

XSSFWorkbook wb = new XSSFWorkbook(fs);
XSSFSheet sheet = wb.getSheetAt(0);

I have created an XSSFSheet object, and it takes wb.getSheetAt(0), my query is why should I pass the wb.getSheetAt(0) to the sheet object. when I try to create an object as below

XSSFSheet sheet = new XSSFSheet(wb);

I get an error stating 

XSSFSheet(org.apache.poi.openxml4j.opc.PackagePart) has protected access in 'org.apache.poi.xssf.usermodel.XSSFSheet'

I looked at the XSSFSheet source code and its constructor has been declared as protected. I am under the impression that an object can be created using the new keyword. What am I missing?

Source code for reference

package ReadAndWrite;

import ReadExcelLibrary.ReadExcelSheet;
import org.apache.poi.xssf.usermodel.XSSFSheet;
import org.apache.poi.xssf.usermodel.XSSFWorkbook;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;


/**
 * Created by Shravya on 11/5/17.
 */
public class ReadExcel {

    public static void main(String[] args) throws Exception {

        File file = new File("//Development//Selenium//ApachePOI//Apache_wb.xlsx");
        FileInputStream fs = new FileInputStream(file);
        XSSFWorkbook wb = new XSSFWorkbook(fs);
        //XSSFSheet sheet = new XSSFSheet(wb);
        XSSFSheet sheet = wb.getSheetAt(0);
        String value = sheet.getRow(0).getCell(0).getStringCellValue();
        System.out.println("The value of cell is " + value);

        ReadExcelSheet excelSheet = new ReadExcelSheet("//Development//Selenium//ApachePOI//Apache_wb.xlsx");
        System.out.println(excelSheet.getData(0,1,1));



    }
}

Upvotes: 0

Views: 317

Answers (1)

JB Nizet
JB Nizet

Reputation: 692181

XSSFSheet sheet = new XSSFSheet(wb);

Let's pretend you can do that. It would create a new XSSFSheet object, that doesn't exist yet.

XSSFSheet sheet = wb.getSheetAt(0);

That doesn't do the same thing at all. That allows getting the already existing sheet that is at index 0 in the workbook. So those are two completely different things. The same difference there is, basically, between getting a car from a garage, and building a brand new car.

So when you say

XSSFSheet sheet = wb.getSheetAt(0);

I have created an XSSFSheet object, and it takes wb.getSheetAt(0)

that's incorrect. You haven't created anything. You have obtained a reference to an existing XSSFSheet object, that the workbook had already created for you.

I am under the impression that an object can be created using the new keyword.

Yes, that's what a constructor allows doing. But if a constructor is protected, it means that only subclasses or classes in the same package are allowed to call the constructor.

To create a new sheet in a workbook, you would use this method, to ask the workbook to create the sheet for you, and give you a reference to the created sheet. Just like, to obtain a new car, you typically don't create one by yourself, but instead ask a car manufacturer to build one for you.

Upvotes: 2

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