The Java Language Specification, Third Edition

8.1.3 Inner Classes and Enclosing Instances CLASSES
182
text. A class C is an inner class of class O if it is either a direct inner class of O or
an inner class of an inner class of O.
A class O is the zeroth lexically enclosing class of itself. A class O is the nth
lexically enclosing class of a class C if it is the immediately enclosing class of the
n – 1 st lexically enclosing class of C.
An instance i of a direct inner class C of a class O is associated with an
instance of O, known as the immediately enclosing instance of i. The immediately
enclosing instance of an object, if any, is determined when the object is created
(§15.9.2).
An object o is the zeroth lexically enclosing instance of itself. An object o is
the nth lexically enclosing instance of an instance i if it is the immediately
enclosing instance of the n –
1 st lexically enclosing instance of i.
When an inner class refers to an instance variable that is a member of a lexically
enclosing class, the variable of the corresponding lexically enclosing
instance is used. A blank final (§4.12.4) field of a lexically enclosing class may
not be assigned within an inner class.
An instance of an inner class I whose declaration occurs in a static context
has no lexically enclosing instances. However, if I is immediately declared within
a static method or static initializer then I does have an enclosing block, which is
the innermost block statement lexically enclosing the declaration of I.
Furthermore, for every superclass S of C which is itself a direct inner class of a
class SO, there is an instance of SO associated with i, known as the immediately
enclosing instance of i with respect to S. The immediately enclosing instance of an
object with respect to its class’ direct superclass, if any, is determined when the
superclass constructor is invoked via an explicit constructor invocation statement.
Any local variable, formal method parameter or exception handler parameter
used but not declared in an inner class must be declared final. Any local variable,
used but not declared in an inner class must be definitely assigned (§16)
before the body of the inner class.
Inner classes include local (§14.3), anonymous (§15.9.5) and non-static member
classes (§8.5). Here are some examples:
class Outer {
int i = 100;
static void classMethod() {
final int l = 200;
class LocalInStaticContext{
int k = i; // compile-time error
int m = l; // ok
}
}
DRAFT