Instantiation of a Listener using an anonymous inner class

[Mark Do]

 JMenuItem blueChoice = new JMenuItem("Blue");
        blueChoice.addActionListener(new InnerMenuListener(){
            public void actionPerformed(ActionEvent e){
                String buttonCommandString = e.getActionCommand( );
                if (buttonCommandString.equals("Red"))
                    redPanel.setBackground(Color.RED);
                else if (buttonCommandString.equals("White"))
                    whitePanel.setBackground(Color.WHITE);
                else if (buttonCommandString.equals("Blue"))
                    bluePanel.setBackground(Color.BLUE);
                else
                    System.out.println("Unexpected error.");
            }
        });

Can a method in an anonymous inner class ever be private? why or why not?

[Jesper de Jong]

Why don't you try out if you can add a private method to the anonymous inner class?

[Mark Do]

I've tried changing it to a private scope, and an error comes up.

I don't understand why it can't be private..

[Maneesh Godbole]

A child class needs to satisfy the super class contract. When you narrow down the scope, you break the conract

[Jesper de Jong]

The actionPerformed method cannot be made private, because it's a method that's inherited from the interface that the anonymous class is inheriting. But this, by itself, has nothing to do with the fact that it's an anonymous inner class. Methods declared in interfaces are always public, so in a class that implements an interface (no metter if it's an anonymous inner class or a regular class), the methods inherited from the interface must always be public.

But you can add private methods if you like, for example:

 JMenuItem blueChoice = new JMenuItem("Blue");
        blueChoice.addActionListener(new InnerMenuListener(){
            public void actionPerformed(ActionEvent e){
                someMethod(); // call the private method

                String buttonCommandString = e.getActionCommand( );
                if (buttonCommandString.equals("Red"))
                    redPanel.setBackground(Color.RED);
                else if (buttonCommandString.equals("White"))
                    whitePanel.setBackground(Color.WHITE);
                else if (buttonCommandString.equals("Blue"))
                    bluePanel.setBackground(Color.BLUE);
                else
                    System.out.println("Unexpected error.");
            }

            private void someMethod() {
                System.out.println("Hello");
            }
        });

[Campbell Ritchie]

Use a different listener for each colour. That block of ifs is in my opinion not object‑oriented. Search my posts in the Swing forum for "ColourListener".

As for Swing forum, I think this discussion would sit better there, so I shall move it.

[Mark Do]

Thanks guys! that can't be any clearer!

[Mark Do]

Is it right to say:
• The parameter ‘e’ can be renamed as long as its type is the same.
• The class that has the interface type InnerMenuListener (deduced from the constructor) is the anonymous class definition in the code.
• actionPerformed CANNOT be renamed because it is implementing an interface, therefore the names are prescribed by the interface.

I'm not too sure how to answer this question though?
What is referenced by ‘e’, the parameter of the actionPerformed(…) method?


Thanks!