In Excel handling how is it that we call getRow without creating object of XSSFSheet class

Question

How is it that we invoke getRow() and getCell() without creating object of XSSFSheet class. To create an object we use new keyword right but without using new keyword how is it that we can call the non static methods getRow() and getCell ()

Ex:
XSSFWorkbook workbook = new XSSFWorkbook(fs);
XSSFSheet sheet = workbook.getSheetAt(0);
Row row = sheet.getRow(0);
Cell cell = row.getCell(0);

As we can see here we are calling getRow() and getCell() without creating object of XSSFSheet class using new keyword.

Answer 1

In Excel file handling using Apache POI, when you call getRow on an XSSFSheet object, you are indeed using an instance of the XSSFSheet class. However, you might not be directly creating this instance using the new keyword yourself; instead, it's often retrieved from an existing XSSFWorkbook object.

Here's a step-by-step explanation of how this typically works:

1. Creating an XSSFWorkbook Instance: First, you create an instance of XSSFWorkbook, which represents an entire Excel workbook. This is usually where you use the new keyword, for example, when creating a new workbook or loading an existing one from a file.

   XSSFWorkbook workbook = new XSSFWorkbook(); // for a new workbook // or XSSFWorkbook workbook = new XSSFWorkbook(new FileInputStream("path_to_excel_file")); // for an existing workbook 

2. Retrieving an XSSFSheet Instance: Once you have the XSSFWorkbook instance, you retrieve an XSSFSheet object from it. This doesn't require the new keyword because the XSSFWorkbook class provides methods to access its sheets, either by name or index. These sheets are already part of the workbook structure.

   XSSFSheet sheet = workbook.getSheetAt(0); // retrieves the first sheet 

3. Using getRow on the XSSFSheet Instance: Now, with the XSSFSheet instance, you can call getRow. The getRow method is an instance method of the XSSFSheet class. It doesn't create a new row but retrieves an existing one from the sheet. If the row doesn't exist, it may return null or create a new row, depending on how the library is implemented.

   Row row = sheet.getRow(0); // retrieves the first row 

In this process, you're not creating a new XSSFSheet object directly; instead, you're obtaining a reference to an existing sheet from the XSSFWorkbook object. The creation and management of the XSSFSheet instances are handled internally by the Apache POI library. This design pattern, where a parent object manages the creation and lifecycle of child objects, is common in object-oriented programming.

Comments

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