Good design with Inner classes

I have a situation where I visualise a large component say X and smaller components in X, say Y and Z which in turn maybe composed of further smaller ones...

Now the simple way to design such beans would be to have instance variables of Y and Z type in X:

Was wondering if it would be good design practice to use Inner classes in this situation. Are there like general guidelines or a rule of hand as to when and when not to use Inner classes? Don't have a lotta experience using Inner classes... Would this complicate the code or cause maintenance issues?

Thanks for your help!

I don't like inner classes (except for some UI stuff) because most developers find them more complicated then regular classes and the inability to define static variables. I wouldn't use them. If you want to hide them from the rest of the program I would give them a package scope and put them in a special package.

Agree with Wouter. Composition can be implemented by means of having an instance variable- HAS-A relationship- The one which you have given as example. Its always better to keep the code simple. And there might be possibility that components Y and Z can exist independently.

Thanks guys,

The case I am dealing with is definitely composition and not aggregation where the inner objects can exist independently - in which case inner classes are definitely a bad idea.
I think I'll go with the instance variables approach - but just for the sake of knowing, would there be anything wrong with the design (keeping aside the complexity) if I used Inner classes? Or is that an acceptable approach too?

The idea of good design is how it is perceived by the developers around. So a good design vouched by few might be a bad design for few others. But there are few good practices around- but I am not aware of anything related to use of Inner classes.