How do you hide a Swing Popup when you click somewhere else

As pajton noted in a previous comment, Popup is not a JComponent to which listeners can be readily bound. But, as its documentation states, "implementations of Popup are responsible for creating and maintaining their own Components to render [its subject] to the user."

So in using it as your presentation mechanism, your Popup is going to have to present itself as an actual Swing component anyway. Have it register itself to that component. Have it hide itself when the component loses focus.

import java.awt.FlowLayout;
import java.awt.Frame;
import java.awt.Point;
import java.awt.event.ActionEvent;
import java.awt.event.WindowEvent;
import java.awt.event.WindowFocusListener;
import javax.swing.JButton;
import javax.swing.JDialog;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.Popup;

public class PopupTester extends JFrame {
    private static class MessagePopup extends Popup
        implements WindowFocusListener
    {
        private final JDialog dialog;

        public MessagePopup(Frame base, String message) {
            super();
            dialog = new JOptionPane().createDialog( base, "Message" );
            dialog.setModal( false );
            dialog.setContentPane( new JLabel( message ) );
        }
        @Override public void show() {
            dialog.addWindowFocusListener( this );
            dialog.setVisible( true );
        }
        @Override public void hide() {
            dialog.setVisible( false );
            dialog.removeWindowFocusListener( this );
        }
        public void windowGainedFocus( WindowEvent e ) {
            // NO-OP
        }

        public void windowLostFocus( WindowEvent e ) {
            hide();
        }
    }

    public static void main(String[] args) {
    final PopupTester popupTester = new PopupTester();
    popupTester.setLayout(new FlowLayout());
    popupTester.setSize(300, 100);
    popupTester.add(new JButton("Click Me") {
      @Override
      protected void fireActionPerformed(ActionEvent event) {
        Point location = getLocationOnScreen();
          MessagePopup popup = new MessagePopup( popupTester, "Howdy" );
          popup.show();
        }
      });
      popupTester.add(new JButton("No Click Me"));
      popupTester.setVisible(true);
      popupTester.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }
}

Use a JPopupMenu. You can add any component to it, not just menu items.

You can add MouseListener to your background panel and hide the popup when somebody clicks on the panel.

To react on application minimization, use WindowListener attached to a JFrame.

Etc, etc. May seem tedious, but surely will work.

Thanks pajton and Noel Ang for getting me pointed in the right direction! Here is the solution that I ended up with. I'm just including it here so that others may benefit from it.

I ended up going with a JWindow since it doesn't get the window decorations but does get focus events.

import java.awt.*;
import java.awt.event.*;

import javax.swing.*;

public class PopupTester extends JFrame {
  private static class MessagePopup extends Popup implements WindowFocusListener {
    private final JWindow dialog;

    public MessagePopup(Frame base, JLabel component, int x, int y) {
      super();
      dialog = new JWindow(base);
      dialog.setFocusable(true);
      dialog.setLocation(x, y);
      dialog.setContentPane(component);
      component.setBorder(new JPopupMenu().getBorder());
      dialog.setSize(component.getPreferredSize());
      dialog.addKeyListener(new KeyAdapter() {
        @Override
        public void keyPressed(KeyEvent e) {
          if (e.getKeyCode() == KeyEvent.VK_ESCAPE) {
            dialog.setVisible(false);
          }
        }
      });
    }

    @Override
    public void show() {
      dialog.addWindowFocusListener(this);
      dialog.setVisible(true);
    }

    @Override
    public void hide() {
      dialog.setVisible(false);
      dialog.removeWindowFocusListener(this);
    }

    public void windowGainedFocus(WindowEvent e) {
      // NO-OP
    }

    public void windowLostFocus(WindowEvent e) {
      hide();
    }
  }

  public static void main(String[] args) {
    final PopupTester popupTester = new PopupTester();
    popupTester.setLayout(new FlowLayout());
    popupTester.setSize(300, 100);
    popupTester.add(new JButton("Click Me") {
      @Override
      protected void fireActionPerformed(ActionEvent event) {
        Point location = getLocationOnScreen();
        int x = (int) location.getX();
        int y = (int) (location.getY() + getHeight());
        JLabel myComponent = new JLabel("Howdy");

        MessagePopup popup = new MessagePopup(popupTester, myComponent, x, y);
        popup.show();
      }
    });
    popupTester.add(new JButton("No Click Me"));
    popupTester.setVisible(true);
    popupTester.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  }
}