Question

Is it bad practice or “dumb” to access methods/fields that are private in the public class from private classes in the same file. In my case I have a method that add components in my GUI to panels(GridBagLayout) so I have made a method for this. However I have three panels so instead of making a addComponent-method in each private class I have the private method addComponent in the public class.

This is a overview of my class:

• RegisterQuestionGUI (public)
  • This class has many methods, one of them is a private method named addComponent.
  • I also have three private classes that extend JPanel, and all of these classes use the addComponent in exactly the same way.

So back to my question, is this a good/bad way of doing it?

Thanks in advance.

Answer 1

In general, I don’t see an issue with it. Private inner classes are part of the implementation of the outer class, so encapsulation is not broken. OTOH getting rid of duplication is a good thing.

AFAIK this idiom is used many times in the class library (it is there for a reason, after all :-), e.g. when implementing Iterators in the Collection Framework. Its typical usage tends to have the following common traits:

• you need to implement a specific interface without publishing the concrete implementation class, however
• the implementation is tightly bound to some public class (making the two in fact a component).

Implementing the interface in a private inner class nicely satisfies both constraints at once, making the logical codependency of the two classes explicit, and encapsulating the implementation class.