How to tidy up a swing listener program?

[Timmy Ryan]

I have a Swing application that has a menu, main JPanel and another JPanel to the right.
The JPanel to the right can be toggled visible or hidden by a menu option.
The menu listener is in a separate class to the menu one.

I create the menu plus the two JPanels in a JFrame class.
What I have at the moment is when I create the MenuBar I pass the rightJPanel reference to it.
Then when I create the menu listener which implements ActionListener I have to pass the rightJPanel to it as well.
In order to be able to set the rightJPanel visible or not.

How do I tidy this up?

Should I have the menu listener class a private class within the body of the menu class?
I kind of want to keep it separate though if at all possible.

[Stephan van Hulst]

I usually make one class for each form, which contains all the listeners as well. Here's how I would recommend you do it:

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

final class MyForm {

  private final JFrame frame;
  private final JPanel mainPanel, rightPanel;

  MyForm() {
    frame = new JFrame();
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    mainPanel = new JPanel();
    frame.add(mainPanel, BorderLayout.CENTER);

    rightPanel = new JPanel();
    frame.add(rightPanel, BorderLayout.EAST);
    rightPanel.setBackground(Color.RED);

    JMenuBar menuBar = new JMenuBar();
    frame.setJMenuBar(menuBar);

    JMenu menu = new JMenu("View");
    menuBar.add(menu);

    Action action = new AbstractAction("Toggle panel") {
      public void actionPerformed(ActionEvent e) {
        togglePanel();
      }
    };

    menu.add(action);

    frame.pack();
    frame.setVisible(true);
  }

  void togglePanel() {
    rightPanel.setVisible(!rightPanel.isVisible());
  }

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

[Timmy Ryan]

Thanks for the response.

After thinking about it I could just have a public static method in the class that creates the rightPanel to toggle it on or off and call this from the menu listener class.
Which is basically what you have done there.

[Stephan van Hulst]

Try to eliminate static members. Globally available operations or data make your classes easier targets for malicious code. Static fields should be reserved for constants, static methods should be utility operations.

Make one instance responsible for maintaining the panels. You should request that instance to hide or display the panels. In my case, an instance of the MyForm class is responsible for the panels.

If you want your listeners in separate classes, you only have to pass them the MyForm instance, and the listeners can call the necessary methods on the instance.