I have a project that I'm working on a project that requires 2 JFrames in a single program. The problem is that when I close one the other will also close so I made a test class to see what the issue was and I still couldn't figure it out so here is the test case that I have:

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

public class frameTest {

    public static void main(String[] args) {

        JFrame f1 = new JFrame();
        JButton open = new JButton("open");
        open.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent arg0) {
                JFrame f2 = new JFrame();
                f2.setVisible(true);
                f2.setDefaultCloseOperation(f2.EXIT_ON_CLOSE);
                f2.setSize(200, 200);
            }
        });

        f1.setDefaultCloseOperation(f1.EXIT_ON_CLOSE);
        f1.setVisible(true);
        f1.setSize(500, 500);
        f1.add(open);
    }
}

When I click the open button the popup (f2) will appear but when I close it the other window will also close, why does this happen?

f2.setDefaultCloseOperation(f2.EXIT_ON_CLOSE);

EXIT_ON_CLOSE means close the Java VM.

If you just want to close the current frame then use:

f2.setDefaultCloseOperation(f2.DISPOSE_ON_CLOSE);