CODEWITHSUNDEEP
javaswingdesign-patterns
Kevvvvyp
Kevvvvyp

Reputation: 1774

When to use inner classes over decoupled design?

I often see people write inner classes for listeners take swing for example.

   button.addActionListener(new ActionListener() {     
        public void actionPerformed(ActionEvent e) {
            //some action
        }
    });

At my uni there is a lot of emphasis on designs being decoupled using design patterns such as MCV or MVP.

When would I want to use an inner class over a decoupled way of doing it?

My only guess is when objects don't need to interact? (Or laziness??)

(Student)

Upvotes: 1

Views: 89

Answers (2)

AsSiDe
AsSiDe

Reputation: 1846

This Kind of Anonymous Inner Classes are called argument-defined inner classes,and automatically instantiated as part of the method invocation.

Here in the method argument, we get an object of a class,which is the subclass of the ActionListener Interface,but the newly created class is without any name(anonymous) so we cannot create its object again after the control passes through this statement.

  1. now in the anonymous inner class which implements ActionPerformed Interface ,we override the actionPerformed() method which is very specific to that button and then new keyword creates an object of this anonymous class and it will automatically passed as argument.

  2. or you may also create a new class(say myListener) which extends ActionListener class and overrides its actionPerformed() method. and then create a new object of myListener and pass it to the addActionListener()method as argument.

if you use metohod 2. you can see if you have 10 buttons and each have to perform different task ,then you have to create 10 ActionPerformed implementor classes and pass object to the addActionListener() method of these implementor classes. It is totally foolish to use this approach to create a whole new class just for a single object.

That's why most Listener are passed as an object of anonymous inner classes.

Upvotes: 0

M A
M A

Reputation: 72854

This is actually called an anonymous inner class. You would use it if you only need to use the class once.

It would also reduce the size of your code unless it overrides many features of course (personally I prefer anonymous classes to be small in size for readability).

Upvotes: 1

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