How to end java program

Question

Do I have to add some exit statement?

Code seems to be running well, but after it finish its task I still can't interact with console.

/*
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 */
package excelb;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Scanner;
import javax.swing.JFileChooser;
import javax.swing.JFrame;


/**
 *
 * @author hp
 */
public class Excelb {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) throws FileNotFoundException, IOException {
        // TODO code application logic here
        String row;
        String row2;
        File fn = null;
        int counter = 0;



        Scanner in = new Scanner(System.in);
        System.out.println("Enter the run identifier for output file");
        String output = in.nextLine();


        //input
        JFileChooser jFileChooser = new JFileChooser();
        jFileChooser.setCurrentDirectory(new File("C:/"));

        int result = jFileChooser.showOpenDialog(new JFrame());


        if (result == JFileChooser.APPROVE_OPTION) {
             fn=jFileChooser.getSelectedFile();
            System.out.println("Data file: " + fn.getAbsolutePath());
            //System.out.println("Data file: " + fn.getTitle());
        }



        BufferedReader csvReader = new BufferedReader(new FileReader("Keywords.csv"));
        BufferedReader csvReader2 = new BufferedReader(new FileReader(fn.getAbsolutePath()));

        row = csvReader.readLine();
        String[] data = row.split(",");
        while (counter < data.length) {
            while ((row2 = csvReader2.readLine()) != null) {
                String[] data2 = row2.split(",");
                for (int j = 0; j < data.length; j++) {
                    if ((data2[data2.length - 1].contains(data[j]))) {
                        //DateFormat df = new SimpleDateFormat("dd/MM/yy");
                        //Date dateobj = new Date();
                        //String d = df.format(dateobj);
                        //d = d.replaceAll("/", "");
                        String newFile = data[j] + "_" + output + ".csv";
                        FileWriter csvWriter = new FileWriter(newFile, true);
                        for (int i = 0; i < data2.length; i++) {
                           csvWriter.append(data2[i]);
                            csvWriter.append(",");
                        }
                        csvWriter.append("\n");
                        csvWriter.close();
                    }
                }
            }
            counter++;
        }
        System.out.println("Finished");
        csvReader.close();
        csvReader2.close();
    }

}

Answer 1

Pshemo's answer explains why your app isn't ending.

But it does fail to make the key point, which is:

To exit a Java app, run System.exit(0); - and consider returning a non-0 value if errors occurred. Don't wait for the JVM to exit itself (it does do so, once the only remaining live threads have the daemon flag set) - that's a frail strategy if the point is to close the app. Just call exit.

Answer 2

Problem:

Your application consists of two separate threads:

1. handling main method
2. handling events from swing events.

Even if main thread will end its execution, swing thread is still running and doesn't allow your application to exit.
BTW that is a good thing. We are building GUI components like frames with buttons, labels, etc. in main method. Now, when main method/thread ends, should application be closed and along with it all built GUI? That wouldn't make much sense.

Why problem appeared?

Because you used new JFrame() which started swing thread responsible for handling events related to swing/AWT components (like button clicks, etc.).

Solutions:

Approach 1: Prevent problem from happening

Don't start swing thread with new JFrame() if you are not planning to create application based on swing GUI.

In your case simple solution would be passing null instead of new JFrame() to jFileChooser.showOpenDialog. This would also let that dialog be placed at the center of the screen:

int result = jFileChooser.showOpenDialog(null);

Approach 2: Forceful exit

To forcefully close your application you can use System.exit(0).

But generally it is better to prevent problems from happening than solving them.