Inner class in interface vs in class

Question

What is the difference between these two innerclass declarations? Also comment on advantages/disadvantages?

case A: class within a class.

public class Levels {      static public class Items {     public String value;     public String path;      public String getValue() {       return value;}   } } 

and case B: class within interface.

public interface Levels{    public class Items {     public String value;     public String path;      public String getValue() {       return value;}   } } 

Made correction: to placement of getvalue method.

further info: I am able to instantiate Items class in both cases A and B in another class that does not implement interface AT ALL.

public class Z{//NOTE: NO INTERFACE IMPLEMENTED here!!!!  Levels.Items items = new Levels.Items(); } 

Since an interface is not instantiated, all the elements inside an interface are accessible by dot notation without LEVELS interface instantiated simply because you cannot instantiate an interface - effectively making a class defined inside an interface permeable to static reference.

So saying that Items class in case B is not static does not make sense. Since both cases A and B are instantiated the same way, I am not looking for semantics on what is static or inner or nested. Stop giving me answers on semantics. I want the compiler, runtime and behavioural differences/advantages, or if none then say so. No more answers on semantics please!!!!! An expert on JVM or .NET VM specification innards please this answer question rather than text book semanticissiests.

Answer 1

An static inner class is a nested class, and the non-static is called an inner class. For more, look here.

However, I like to quote an excerpt from the same link.

A static nested class interacts with the instance members of its outer class (and other classes) just like any other top-level class. In effect, a static nested class is behaviorally a top-level class that has been nested in another top-level class for packaging convenience.

You didn't use the word static in the second case. And you think it would implicitly be static because its an interface. You are right in assuming that.

You can instantiate the inner class in your interface, just like a static nested class, because its really a static nested class.

Levels.Items hello = new Levels.Items(); 

So, the above statement will be valid in both of your cases. Your first case is of static nested class, and in the second case you didn't specify static, but even then it would be an static nested class because its in the interface. Hence, no difference other then the fact that one is nested in a class, and the other in an interface.

Normally an inner class in a class, not in interface, would be instantiated like below.

Levels levels = new Levels(); Levels.Items items = levels.new Items(); 

Moreover, a "non-static" inner class will have a implicit reference to its outer class. This is not the case with "static" nested class.