Alert in JAVA FX
<p>I want to display an alert when a file already exists when trying to create the file with same name . I have not completed the code fully. I want to retrieve the button value Yes/No from the UI . </p>

<p><strong>Code:</strong> </p>

<p>This is how the controller is coded.</p>

<pre><code>package application;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.net.URL;
import java.util.Map;
import java.util.ResourceBundle;
import java.util.Set;
import java.util.TreeMap;

import org.apache.poi.ss.usermodel.Cell;
import org.apache.poi.xssf.usermodel.XSSFRow;
import org.apache.poi.xssf.usermodel.XSSFSheet;
import org.apache.poi.xssf.usermodel.XSSFWorkbook;

import javafx.event.ActionEvent;
import javafx.fxml.FXML;
import javafx.fxml.FXMLLoader;
import javafx.fxml.Initializable;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.stage.Stage;

public class WarningController implements Initializable {
    @FXML
    public Button yes;

    @FXML
    public Button no;

    public static String type;

    @Override
    public void initialize(URL arg0, ResourceBundle arg1) {
        // TODO Auto-generated method stub

    }

     public String confirmSelection(ActionEvent event)throws IOException{
         Button button = (Button) event.getSource();
             type = button.getText();
            if(type.equals("Yes")){
                Stage stage = (Stage) yes.getScene().getWindow();
                stage.close();
                //System.out.println("Yes");
                return type;
            }
            else{
                //System.out.println("No");
                Stage stage1 = (Stage) no.getScene().getWindow();
                stage1.close();
                return type;
            }

     }
/********************************************************************************/
     public void writesheet(String[][] result,String ComboValue,String[] heading) throws IOException{ 
            //Create blank workbook
            XSSFWorkbook workbook = new XSSFWorkbook(); 
            //Create a blank sheet
            XSSFSheet spreadsheet = workbook.createSheet( " Employee Info ");
            //Create row object
            XSSFRow row;

            String[][] towrite=result;
            int rows=towrite.length;
            //int cols=towrite[0].length;
           // System.out.println(rows +"    "+ cols);

            Map &lt; String, Object[] &gt; empinfo = new TreeMap &lt; String, Object[] &gt;();
            empinfo.put("0", heading);
            for(int i=1;i&lt;=rows;i++){
                empinfo.put( Integer.toString(i),towrite[i-1]);
            }


            //Iterate over data and write to sheet
            Set &lt; String &gt; keyid = empinfo.keySet();
            int rowid = 0;
            for (String key : keyid)
            {
               row = spreadsheet.createRow(rowid++);
               Object [] objectArr = empinfo.get(key);
               int cellid = 0;
               for (Object obj : objectArr)
               {
                  Cell cell = row.createCell(cellid++);
                  //cell.setCellValue((String)obj);
                  cell.setCellValue(obj.toString());
               }
            }

            //Write the workbook in file system
            File f=new File(("C:\\"+ComboValue+".xlsx"));
            if(f.exists()){
                Stage primaryStage=new Stage();
                Parent root=FXMLLoader.load(getClass().getResource("/application/Warning.fxml"));
                Scene scene = new Scene(root,350,150);
                scene.getStylesheets().add(getClass().getResource("application.css").toExternalForm());
                primaryStage.setScene(scene);
                primaryStage.show();
                System.out.println(type);
            }
            FileOutputStream out = new FileOutputStream(f);
            workbook.write(out);
            out.close();
            System.out.println(ComboValue+"  "+"Excel document written successfully" );
            workbook.close();
            }


}
</code></pre>

<p>I want to use button value(stored in String type) in writesheet function. Now it is returning NULL.</p>

<p>Please suggest if there is any other way to show warning.I am using two fxml files and this is the second excel file.</p>

<p><a href="https://i.stack.imgur.com/ZK6UC.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ZK6UC.jpg" alt="enter image description here"></a></p>

<pre><code>  [1]: http://i.stack.imgur.com/ZK6UC.jpg
</code></pre>