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What is static nested class and usage in Java

Question -What is static nested class and usage in Java

Solutions– Many developers are confused and telling static nested class as static inner class.But in java, there is no static inner class. 😮

Ok.First we understand ,

what is inner class – inner class or nested class is a class declared entirely within the body of another class or interface.An instance of a normal or top-level class can exist on its own. By contrast, an instance of an inner class cannot be instantiated without being bound to a top-level class.

class OuterClass {

  class InnerClass {  }

}

Types of nested classes in Java

Member class – They are declared outside a function (hence a “member”) and not declared “static”.
Local class
Anonymous class

Nested or inner class is a member of its enclosing class.
Non-static nested classes (inner classes) have access to other members of the enclosing class, even if they are declared private. Static nested classes do not have access to other members of the enclosing class.A static nested class interacts with the instance members of its outer class (and other classes) just like any other top-level class. In effect, a static nested class is behaviorally a top-level class that has been nested in another top-level class for packaging convenience.

Why we use– if a class does’nt depend on anything other than his outer class then we will create static nested class.for example – we have nThere is no need for LinkedList.Entry to be top-level class as it is only used by LinkedList (there are some other interfaces that also have static nested classes named Entry, such as Map.Entry – same concept). And since it does not need access to LinkedList’s members, it makes sense for it to be static – it’s a much cleaner approach.

Happy learning with Vinay in techartifact…

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Setting Styles & Formula in excel file using Apache POI

Requirement – Setting styles on excel cells

Solutions– You can set FONT,Color, Bold etc.Use cell.setCellStyle(style) method.

Following is code for setting styles

HSSFWorkbook workbook = new HSSFWorkbook();
HSSFSheet sheet = workbook.createSheet("Style example");
<strong> //Example 1 of setting styles in cell</strong>
HSSFFont font = workbook.createFont();
font.setBoldweight(HSSFFont.BOLDWEIGHT_BOLD);
font.setFontName(HSSFFont.FONT_ARIAL); 
HSSFCellStyle style = workbook.createCellStyle();
style.setFont(font);
 
Row row = sheet.createRow(0);
Cell cell = row.createCell(0);
cell.setCellValue("Setting text in BOLD and in Arial font");
cell.setCellStyle(style);
 
<strong>  //Example 2 of setting styles in cell</strong>
font = workbook.createFont();
font .setItalic(true);  // setting cell value as italic
font setFontHeightInPoints((short) 12);   //setting font height.
font.setColor(HSSFColor.GREEN.index);  // setting color as green
style = workbook.createCellStyle();
style.setFont(font);
 
row = sheet.createRow(1);
cell = row.createCell(0);
cell.setCellValue("Setting text in italic & green");
cell.setCellStyle(style);
 
try {
    FileOutputStream out = new FileOutputStream(new File("C:\\Vinaystyle.xls"));
    workbook.write(out);
    out.close();
    System.out.println("Excel written successfully..");
     
} catch (FileNotFoundException e) {
    e.printStackTrace();
} catch (IOException e) {
    e.printStackTrace();
}

You can also set the background color for the rows as well in sheet

  // Aqua background
CellStyle style = wb.createCellStyle();
style.setFillBackgroundColor(IndexedColors.AQUA.getIndex());
style.setFillPattern(CellStyle.BIG_SPOTS);
row.setRowStyle(style);

Setting Formula in Excel –

    Row row= sheet.createRow(1);
    row.createCell(0).setCellValue(100);
    rpw.createCell(1).setCellValue(200);
    row.createCell(2).setCellValue(300);
    row.createCell(3).setCellFormula("SUM(A1:A4)");
  or 
    cell.setCellFormula("A2*B3*C4")

For evaluating formula you can use –

FormulaEvaluator evaluator = 
workbook.getCreationHelper().createFormulaEvaluator();

evaluateFormulaCell(Cell cell) will check to see if the supplied cell is a formula cell. If it isn’t, then no changes will be made to it. If it is, then the formula is evaluated. The value for the formula is saved alongside it, to be displayed in excel. The formula remains in the cell, just with a new value.

Happy coding with Vinay in techartifact

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Write an excel file in java using Apache POI

Requirment – How to write an excel file in Java

Solutions– Well Apache POI is answer.This API will help you a lot.you have to download and add the POI JAR file to your project’s class path. The Apache POI JAR file can be found http://poi.apache.org/download.html

Following is code –

public static void main(String[] args) throws IOException {
     
    // Directory path where the xls file will be created
    String filePath = "C:/Vinay/ApachePoi/VinayExcel.xls";
    FileOutputStream fout = new FileOutputStream(filePath );
    ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
    HSSFWorkbook workBook = new HSSFWorkbook();
 
    // Create the spreadsheet
    HSSFSheet spreadSheet = workBook.createSheet("vinay_sheet");
     
    // Create the first row
    HSSFRow row = spreadSheet.createRow((short) 0);
     
    // Create the cells and write to the file
    HSSFCell cell;
     
    cell = row.createCell(0);
    cell.setCellValue(new HSSFRichTextString("Vinay"));
    cell = row.createCell(1);
    cell.setCellValue(new HSSFRichTextString("Kumar"));
     
    workBook.write(outputStream);
     
    outputStream.writeTo(fout);
    outputStream.close();
    fout.close();
}

Happy coding with Vinay in techartifact