Check out example codes for "how to add a new row of data in excel using java". It will help you in understanding the concepts better.

Code Example 1

package net.codejava.excel;
 
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
 
import org.apache.poi.EncryptedDocumentException;
import org.apache.poi.openxml4j.exceptions.InvalidFormatException;
import org.apache.poi.ss.usermodel.Cell;
import org.apache.poi.ss.usermodel.Row;
import org.apache.poi.ss.usermodel.Sheet;
import org.apache.poi.ss.usermodel.Workbook;
import org.apache.poi.ss.usermodel.WorkbookFactory;
 
/**
 * This program illustrates how to update an existing Microsoft Excel document.
 * Append new rows to an existing sheet.
 * 
 * @author www.codejava.net
 *
 */
public class ExcelFileUpdateExample1 {
 
 
    public static void main(String[] args) {
        String excelFilePath = "JavaBooks.xls";
         
        try {
            FileInputStream inputStream = new FileInputStream(new File(excelFilePath));
            Workbook workbook = WorkbookFactory.create(inputStream);
 
            Sheet sheet = workbook.getSheetAt(0);
 
            Object[][] bookData = {
                    {"The Passionate Programmer", "Chad Fowler", 16},
                    {"Software Craftmanship", "Pete McBreen", 26},
                    {"The Art of Agile Development", "James Shore", 32},
                    {"Continuous Delivery", "Jez Humble", 41},
            };
 
            int rowCount = sheet.getLastRowNum();
 
            for (Object[] aBook : bookData) {
                Row row = sheet.createRow(++rowCount);
 
                int columnCount = 0;
                 
                Cell cell = row.createCell(columnCount);
                cell.setCellValue(rowCount);
                 
                for (Object field : aBook) {
                    cell = row.createCell(++columnCount);
                    if (field instanceof String) {
                        cell.setCellValue((String) field);
                    } else if (field instanceof Integer) {
                        cell.setCellValue((Integer) field);
                    }
                }
 
            }
 
            inputStream.close();
 
            FileOutputStream outputStream = new FileOutputStream("JavaBooks.xls");
            workbook.write(outputStream);
            workbook.close();
            outputStream.close();
             
        } catch (IOException | EncryptedDocumentException
                | InvalidFormatException ex) {
            ex.printStackTrace();
        }
    }
 
}

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