处理JDialog后JVM不会关闭

Question

I have created an extension of JDialog .

public class ImageDialog extends JDialog implements ActionListener {
    private JTextField textField;

    public ImageDialog(JFrame parent, String title, 
                        String message, BufferedImage bufferedImage) {
        super(parent, title, true);
        if (parent != null) {
            Dimension parentSize = parent.getSize();
            Point p = parent.getLocation();
            setLocation(p.x + parentSize.width / 4, p.y + parentSize.height / 4);
        }

        this.setDefaultCloseOperation(WindowConstants.DISPOSE_ON_CLOSE);
        this.setModal(true);

        JPanel frame = new JPanel();
        frame.setLayout(new BoxLayout(frame, BoxLayout.Y_AXIS));

        frame.add(new JLabel(message), BorderLayout.PAGE_START);

        JLabel lblimage = new JLabel(new ImageIcon(bufferedImage));
        frame.add(lblimage, BorderLayout.CENTER);

        textField = new JTextField(1);

        frame.add(textField, BorderLayout.PAGE_END);

        getContentPane().add(frame);

        JPanel buttonPane = new JPanel();
        JButton button = new JButton("OK");
        buttonPane.add(button);
        button.addActionListener(this);
        getContentPane().add(buttonPane, BorderLayout.SOUTH);
        setDefaultCloseOperation(DISPOSE_ON_CLOSE);
        pack();
        setVisible(true);
    }

    public String getTextField() {
        return textField.getText();
    }

    public void actionPerformed(ActionEvent e) {
        setVisible(false);
        dispose();
    }
}

It works well and does what's it supposed to do, except that jvm won't close after it's been used. I use it as follows:

ImageDialog dlg = new ImageDialog(new JFrame(), "Important question", "How many fluffy bunnies do you see?", img);
System.out.println(dlg.getTextField());
dlg.dispose();

But JVM just hangs there when the program is done. Is there any way to fix this?

Answer 1

You need to set for your frame setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);

Or in any other place:

frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);

After closing dialog program will exit.

For dialog you should set DISPOSE_ON_CLOSE close operation property. Dialog is frame dependent. Your program will end when you close your frame.

That's why don't forget to make your frame visible.

EDIT

Instead of this:

ImageDialog dlg = new ImageDialog(new JFrame(), "Screen captcha", "Enter the letters from the image", img);
System.out.println(dlg.getTextField());
dlg.dispose();

You should have sth like this:

JFrame f = new JFrame();
f.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
f.setVisible(true);
//ideally frame should have a button that creates the dialog and sets it to visible
// no need to dispose dialog here

Answer 2

It seems to work just fine in this SSCCE that uses DISPOSE_ON_CLOSE for the dialogs as well as the frame.

Note: When the last displayable window within the Java virtual machine (VM) is disposed of, the VM may terminate.

That note is important if the app. uses DISPOSE_ON_CLOSE consistently and the VM fails to terminate. It indicates that there is a stray non-daemon thread running (amok?). Better to find the source of that thread and take reasonable action to terminate it gracefully.

import java.awt.*;
import java.awt.event.*;
import java.awt.image.*;
import javax.swing.*;

public class ImageDialog extends JDialog implements ActionListener {
    private JTextField textField;

    public static void main(String[] args) {
        JFrame f = new JFrame("Image Dialog Test");
        BufferedImage bi = new BufferedImage(128,50,BufferedImage.TYPE_INT_RGB);
        f.setLocationByPlatform(true);
        f.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        f.setSize(400,100);
        f.setVisible(true);
        new ImageDialog(f, "Hi!", "Hello World", bi);
    }

    public ImageDialog(JFrame parent, String title, 
                        String message, BufferedImage bufferedImage) {
        super(parent, title, true);
        if (parent != null) {
            Dimension parentSize = parent.getSize();
            Point p = parent.getLocation();
            setLocation(p.x + parentSize.width / 4, p.y + parentSize.height / 4);
        }

        this.setDefaultCloseOperation(WindowConstants.DISPOSE_ON_CLOSE);
        this.setModal(true);

        JPanel frame = new JPanel();
        frame.setLayout(new BoxLayout(frame, BoxLayout.Y_AXIS));

        frame.add(new JLabel(message), BorderLayout.PAGE_START);

        JLabel lblimage = new JLabel(new ImageIcon(bufferedImage));
        frame.add(lblimage, BorderLayout.CENTER);

        textField = new JTextField(1);

        frame.add(textField, BorderLayout.PAGE_END);

        getContentPane().add(frame);

        JPanel buttonPane = new JPanel();
        JButton button = new JButton("OK");
        buttonPane.add(button);
        button.addActionListener(this);
        getContentPane().add(buttonPane, BorderLayout.SOUTH);
        setDefaultCloseOperation(DISPOSE_ON_CLOSE);
        pack();
        setVisible(true);
    }

    public String getTextField() {
        return textField.getText();
    }

    public void actionPerformed(ActionEvent e) {
        setVisible(false);
        dispose();
    }
}

Answer 3

 //Set all your:
 .DISPOSE_ON_CLOSE
 //to: 
 .EXIT_ON_CLOSE
 //and if  dispose(); is the last thing to happen change it to:
 System.exit(0);

EDIT for comment answer:

 System.gc();
 dialog.setVisible(false);

The JVM will run as long as your program is running so I don't see the issue with that.