Program doesn't wait for modal dialog - jfilechooser

Question

With this program I am attempting to have the user select a text file that is a representation of a 4x4 sudoku problem. My agent will then take this file and attempt to solve the sudoku puzzle.
The problem I'm running into is that I can't seem to figure out how to get the proper file selected, and then passed into the method call for processing.
This is the file selector class I've created. So far it successfully brings up a button, and when clicked brings up the computer's file structure so the user can select a file.
import javax.swing.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.File;
/**
* Created by neil on 7/12/17.
*/
public class file_selector {
public JPanel panel1;
public File file;
JButton button1;
public file_selector() {
final JFileChooser fc = new JFileChooser();
button1.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
int returnVal = fc.showOpenDialog(null);
if (returnVal == JFileChooser.APPROVE_OPTION) {
file = fc.getSelectedFile();
System.out.println("You chose to open " + file.getName());
}
}
});
}
public File getFile() {
return file;
}
}
This is my main method in which I attempt to use the file that the user selected. When I put the function calls in a while loop (like it is currently) it never proceeds because the file is never set. If I don't put the function calls in a while loop, I get a nullPointerException error when I try to process the file because the file has a null value.
public class sudoku {
//create 2d array that represents the 16x16 world
public cell[][] world_array = new cell[15][15];
static File myFile;
ArrayList<String> world_constraints;
public static void main(String[] args) throws IOException {
JFrame frame = new JFrame("file_selector");
file_selector fs = new file_selector();
frame.setContentPane(fs.panel1);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.pack();
frame.setVisible(true);
myFile = fs.getFile();
while(myFile != null) {
sudoku my_puzzle = new sudoku();
my_puzzle.solve_puzzle();
}
}
I've done a ton of searching and can't seem to find what's wrong with my file_selector class such that it isn't setting the user selected value for the file.

Answer 1

You call getFile immediately after showing the frame and before the user has opportunity to click anything. Since the condition for while is false, the loop ends immediately and the method doesn't do anything afterwards, in particular it never calls getFile again.
Two options:
Make the button solve the puzzle, not just set file (easier, just change actionPerformed method).
Make file_selector emit an event when a file is selected and add a listener to it (this can be a challenge for you).