Bloch Effective Java - favor static classes over nonstatic - how many instances?

Question

I want to know how many instances of a static member class can be created by the enclosing class. I assume one only, but then the following extract from Bloch doesn\'t make

Answer 1

Yes, you can have many instances of the nested class, no matter that the nested class is static.

When the nested class is static you can create instances of it without having an instance of the enclosing class, this is one of the benefits, and basically the main difference between static and non-static nested classes.

Does this mean then that a static member class is not actually instantiated when the enclosing object is instantiated?

It's instantiated when it's constructor is called. Not any different from non-static classes. The nested class itself is loaded by the JVM, when the code first accesses it. Again this is not any different when compared to other classes, I think (not 100% sure of this though, but you can test it yourself). So I think you're kind of mixing the terms "loading the class by the JVM" and "instantiating the class".

Well in that case, what's the point of Map using a static member class for Entry? Why not just use an interface on the API?

As said, it's easier to create instances of static nested classes. You don't need an enclosing instance which is sometimes (maybe most of the times) exactly what you want.

See also:

(1) Nested Classes

(2) How can the JVM decide if a class is nested into another class?

(3) Loading of a nested class by the JVM

You can search for other references along these lines.
The reference (2) seems advanced and kind of peripheral to your question.