Workbook wb = new HSSFWorkbook();
Sheet sheet = wb.createSheet("Sheet1");
//sets the print area for the first sheet
wb.setPrintArea(0, "$A$1:$C$2");

//Alternatively:
wb.setPrintArea(
        0, //sheet index
        0, //start column
        1, //end column
        0, //start row
        0  //end row
);

// Instantiating a Workbook object
Workbook workbook = new Workbook();

// Accessing the first worksheet in the Workbook file
WorksheetCollection worksheets = workbook.getWorksheets();
Worksheet sheet = worksheets.get(0);

// Obtaining the reference of the PageSetup of the worksheet
PageSetup pageSetup = sheet.getPageSetup();

// Specifying the cells range (from A1 cell to F20 cell) of the print area
pageSetup.setPrintArea("A1:F20");