ActionListener call blocks MouseClick event

Question

I have a window with a MenuItem "maddbound3" with the following ActionListener:

maddbound3.addActionListener
(
    new ActionListener()
    {
        public void actionPerformed(ActionEvent e)
        { 
            menu_addbound3();
        } 
    }
);

When the menu is clicked this listener calls menu_addbound3() below:

void menu_addbound3()
{
    while(getEditMode() != EditMode.NONE)
    {
        System.out.println("!... " + getEditMode());

        synchronized(this)
        {
            try
            {
                wait();
            }
            catch(InterruptedException e)
            {
                e.printStackTrace();
            }
        }
    }
}

A MouseClicked event alters the value of the edit mode and issues a notifyAll() so that the while loop should exit. However, tests have shown that when the system is running through the while loop, the MouseClicked event never occurs on clicking the mouse.

Does the ActionListener block the MouseClicked event? How can I resolve this issue?

Thanks

Answer 1

Don't have a while(true) on the Swing event thread, and likewise don't call wait() on the Swing event thread -- you'll freeze the whole GUI making it completely unresponsive. You need to understand that the main Swing event thread or "event dispatch thread" is responsible for all Swing drawing and user interaction, and so if you tie it up with long-running or freezing code, you lock your entire GUI.

Instead, change the state of your program -- perhaps by setting a variable or two, and have the behavior of your program depend on this state. If you need more specific advice, please tell us what behavior you're trying to achieve, and we can perhaps give you a better way of doing it.

For more on the Swing event thread, please read: Lesson: Concurrency in Swing

Edit
You state:

When the user clicks the menu item I want to obtain information via a series of "discrete" mouse clicks from the window. Hence, on clicking the menu, the user would be prompted to "select a point in the window". So, what I need is for my ActionListener function (menu_addbound3) to then wait for a mouse click. Hence the wait/notify setup. A mouse click changes the edit_mode and notifyAll() causes the wait in the while loop to exit which then causes the while loop to exit and I can then prompt for my next bit of information within the menu_addbound3 function, repeating this as as I need to.

Thanks for the clarification, and now I can definitely tell you that you are doing it wrong, that you most definitely do not want to use the while loop or wait or notify. There are many ways to solve this issue, one could be to use some boolean or enum variables to give the program a state and then alter its behavior depending on the state. Your EditMode enum can be used in the MouseListener to let it know that its active, and then you could also give the MouseListener class a boolean variable windowPointSelected, set to false, and then only set it true after the first click has been made.

Edit 2
For example:

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Point;
import java.awt.event.ActionEvent;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;

import javax.swing.*;

@SuppressWarnings("serial")
public class ProgState extends JPanel {
   private static final int PREF_W = 400;
   private static final int PREF_H = PREF_W;
   private static final Color EDIT_COLOR = Color.red;
   private EditMode editMode = EditMode.NONE;
   private boolean firstPointSelected = false;
   private JMenuBar jMenuBar = new JMenuBar();
   private JTextField firstPointField = new JTextField(15);
   private JTextField secondPointField = new JTextField(15);

   public ProgState() {
      add(firstPointField);
      add(secondPointField);

      JMenu menu = new JMenu("Menu");
      menu.add(new JMenuItem(new AbstractAction("Edit") {

         @Override
         public void actionPerformed(ActionEvent arg0) {
            setEditMode(EditMode.EDITING);
            setFirstPointSelected(false);
         }
      }));
      jMenuBar.add(menu);

      addMouseListener(new MouseAdapter() {

         @Override
         public void mousePressed(MouseEvent mEvt) {
            if (getEditMode() == EditMode.EDITING) {
               Point p = mEvt.getPoint();
               String pStr = String.format("[%d, %d]", p.x, p.y);
               if (!isFirstPointSelected()) {
                  firstPointField.setText(pStr);
                  setFirstPointSelected(true);
               } else {
                  secondPointField.setText(pStr);
                  setEditMode(EditMode.NONE);
               }
            }
         }

      });
   }

   public void setEditMode(EditMode editMode) {
      this.editMode = editMode;

      Color c = editMode == EditMode.NONE ? null : EDIT_COLOR;
      setBackground(c);
   }

   public EditMode getEditMode() {
      return editMode;
   }

   public void setFirstPointSelected(boolean firstPointSelected) {
      this.firstPointSelected = firstPointSelected;
   }

   public boolean isFirstPointSelected() {
      return firstPointSelected;
   }

   @Override
   public Dimension getPreferredSize() {
      return new Dimension(PREF_W, PREF_H);
   }

   public JMenuBar getJMenuBar() {
      return jMenuBar;
   }

   private static void createAndShowGui() {
      ProgState progState = new ProgState();

      JFrame frame = new JFrame("EditMode");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.getContentPane().add(progState);
      frame.setJMenuBar(progState.getJMenuBar());
      frame.pack();
      frame.setLocationRelativeTo(null);
      frame.setVisible(true);
   }

   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            createAndShowGui();
         }
      });
   }
}

enum EditMode {
   NONE, EDITING
}