How does inner class access outter class functions?

[Siegfried Heintze]

This program works. How can I eliminate the reference "me" on line 6 and use line 10 instead of line 9 to add the button? I think line 10 should work but it causes a syntax error.
Thanks!
Siegfried

package components;
import javax.swing.*;
import java.awt.event.*;
public class ButtonDemo extends JPanel{
    protected int count = 0;                          /*   5*/ 
    protected ButtonDemo me = this;
    public ButtonDemo() {
        ((new JButton("push me", null){{
            me.add(this);
            //this.ButtonDemo.add(this);              /*  10*/ 
        }})).addActionListener(new ActionListener(){
                public void actionPerformed(ActionEvent e) {
                    System.out.println("count ="+(count++)+" "+new java.util.Date());
                }
        });                                           /*  15*/ 
    }

    /**
     * Create the GUI and show it.  For thread safety, 
     * this method should be invoked from the         /*  20*/ 
     * event-dispatching thread.
     */
    private static void createAndShowGUI() {

        //Create and set up the window.               /*  25*/ 
        JFrame frame = new JFrame("ButtonDemo");
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);

        //Create and set up the content pane.
        ButtonDemo newContentPane = new ButtonDemo(); /*  30*/ 
        newContentPane.setOpaque(true); //content panes must be opaque
        frame.setContentPane(newContentPane);

        //Display the window.
        frame.pack();                                 /*  35*/ 
        frame.setVisible(true);
    }
    public static void main(String[] args) {
        //Schedule a job for the event-dispatching thread:
        //creating and showing this application's GUI./*  40*/ 
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGUI(); 
            }
        });                                           /*  45*/ 
    }
}

[Mike Simmons]

Try replacing "this.ButtonDemo" with "ButtonDemo.this".

[Siegfried Heintze]

Great! Now it works in Java with your suggested change!

Why does it not work in groovy console 1.7.8 with your suggested change?

Why does line 9 work in java but not groovy 1.7.8?

Thanks,
Siegfried

[Mike Simmons]

I don't know. It works fine in Groovy 1.7.5 using groovyc. Well, you also have to fix the comment on line 20, but that was true in Java as well. What error message do you get? Maybe there's a bug in 1.7.8.

[Siegfried Heintze]

I get the same error from groovyc and groovyconsole.

Exception in thread "AWT-EventQueue-0" 
java.lang.NullPointerException: Cannot invoke method add() on null object
	at org.codehaus.groovy.runtime.NullObject.invokeMethod(NullObject.java:77)
	at org.codehaus.groovy.runtime.callsite.PogoMetaClassSite.call(PogoMetaClassSite.java:45)
	at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:40)
	at org.codehaus.groovy.runtime.callsite.NullCallSite.call(NullCallSite.java:32)
	at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:40)
	at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:116)
	at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:124)
	at components.ButtonDemo$1.<init>(ConsoleScript38:34)


.....

[Mike Simmons]

I ran this past a Groovy-oriented co-worker, and we found that (a) earlier versions of Groovy didn't really support nested/inner classes at all, (b) the current Groovy versions mostly support them now, but (c) the OuterClass.this syntax is still not supported by Groovy. Maybe it will be in the future, but so far, no.

Looking further at your code, it's not clear why you might need this anyway. You basically are doing three things with the button:

1. Create a button.
2. Add it to the JPanel
3. Add an action listener.

There's no reason this all has to be done inside an instance initializer of an anonymous class, though. That's just needlessly confusing to me. (And to Groovy, apparently.) How about:

import javax.swing.*;

import java.awt.event.*;

public class ButtonDemo extends JPanel {
  protected int count = 0;

  public ButtonDemo() {
    JButton button = new JButton("push me", null);
    button.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent e) {
        System.out.println("count =" + (count++) + " " + new java.util.Date());
      }
    });
    add(button);
  }

  private static void createAndShowGUI() {

    //Create and set up the window.
    JFrame frame = new JFrame("ButtonDemo");
    frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);

    //Create and set up the content pane.
    ButtonDemo newContentPane = new ButtonDemo();
    newContentPane.setOpaque(true); //content panes must be opaque
    frame.setContentPane(newContentPane);

    //Display the window.
    frame.pack();
    frame.setVisible(true);
  }

  public static void main(String[] args) {
    createAndShowGUI();
  }
}

I also removed the stuff about doing everything in the event dispatch thread. That seems unnecessary given that the button hasn't been displayed yet - that's the last thing that happens in this code. It makes little difference in this app, but in general I would avoid putting too much in the event dispatch thread - at least, unnecessary stuff - because that's what slows down your app's reaction to everything else that might happen.

My co-worker also offered this more Groovy version of the code (does not work as Java):

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

public class ButtonDemo extends JPanel{
    protected int count = 0;
    public ButtonDemo() {
      def button = new JButton("push me", null)
      add(button)
      def listener = { e -> println "count ="+(count++)+" "+new java.util.Date() } as ActionListener
      button.addActionListener(listener)
    }

    private static void createAndShowGUI() {

        def frame = new JFrame("ButtonDemo");
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);

        //Create and set up the content pane.
        def newContentPane = new ButtonDemo();
        newContentPane.setOpaque(true); //content panes must be opaque
        frame.setContentPane(newContentPane);

        //Display the window.
        frame.pack();
        frame.setVisible(true);
    }
    public static void main(String[] args) {
        createAndShowGUI();
    }
}

But really, if you're using Groovy, you probably want SwingBuilder - you code will be much nicer.

[Siegfried Heintze]

Thank you very much!
Yes -- I've been trying to get my head around swingbuilder for a while.

OK, we are continuing to talk about Groovy here instead of Java....
I don't understand how that "as ActionListener" works when we only give it one function.
Can you translate this into groovy for me so I can better understand how that works?

Thanks,
siegfried

        ((new JTextField("hello, World!", 22){{ButtonDemo.this.add(this);}})).
            addKeyListener(new KeyAdapter() { 
               public void keyReleased(KeyEvent e) { System.out.println("r "+ new java.util.Date() + "text = "+ ((JTextField) e.getSource()).getText());} 
               public void keyTyped(KeyEvent e) { System.out.println("t "+ new java.util.Date() + "text = "+ ((JTextField) e.getSource()).getText());} 
 
               public void keyPressed(KeyEvent e) { System.out.println("p "+ new java.util.Date() + "text = "+ ((JTextField) e.getSource()).getText());} 
 
         });

[Mike Simmons]

Siegfried Heintze wrote:I don't understand how that "as ActionListener" works when we only give it one function.

Well, ActionListener only has one method, so I guess Groovy translates the one code block into an ActionListener implementation that uses the code block as the implementation of the one method. If ActionListener had more than one method, this probably wouldn't work.

I'm not really a Groovy programmer though, so maybe it would be better to ask these questions in the CodeRanch Groovy forum. Or perhaps some nice moderator-type will move the thread over there for you.

[James Ervin]

Mike Simmons wrote:

Siegfried Heintze wrote:I don't understand how that "as ActionListener" works when we only give it one function.

Well, ActionListener only has one method, so I guess Groovy translates the one code block into an ActionListener implementation that uses the code block as the implementation of the one method. If ActionListener had more than one method, this probably wouldn't work.

I'm not really a Groovy programmer though, so maybe it would be better to ask these questions in the CodeRanch Groovy forum. Or perhaps some nice moderator-type will move the thread over there for you.

I'm the Groovy Oriented Co-worker and what Mike describes is essentially true.

In the case where you have an interface that has more than one method you can do the following. You would take a map with the keys as the method names, the values as a closure representing the method body and then use the 'as' operator to coerce it into the appropriate interface. This method is really cool for quick stubbing in tests.