Initialization of Java - Class v/s Interface

Question

I am stuck at the below concept of initialization of java class and interface :

I read the following sentence in the below mentioned book :

An interface is initialized only because a non-constant field declared by the interface is used, never because a subinterface or class that implements the interface needs to be initialized.
But that isn't the case when we initialise any java class.

Thus, initialization of a class requires prior initialization of all its superclasses, but not its superinterfaces.
Initialization of an interface does not require initialization of its superinterfaces.

My question is Why is this so ?

Any help would be greatly appreciated !

Thanks

PS : Book - "Inside the Java Virtual Machine" by Bill Venners (Chapter 7 - LifeTime of a class )

Answer 1

The only things you can declare in an interface are method signatures and constant fields. The latter can be initialized using constant values (i.e. string literals, integers, etc., possibly in some combination) or using non-constant values (i.e. method calls). Thus if an interface doesn't have any non-constant fields, no initialization is required -- everything is known at compile time. If there are non-constant fields that are used by the program, initialization code must be run to ensure those fields are assigned a value.

Hope that helps.

P.S.: That chapter is available online here if anyone wants to read it in full.