|Contents | Prev | Next||Inner Classes Specification|
Here are the extensions to the class body and block syntax:
A type which is a type member is inherited by subtypes, and may be hidden in them by type declarations of the same name. (Types are never "virtual.") Members which are types may be declared
static member class, or a class defined by a block or expression, is an
inner class. All other classes are top-level. Inner classes may not declare
static initializers, or member interfaces. Package
members are never
static. But a class which is a member of a top-level class
may be declared
static, thereby declaring it also to be a top-level class.
Interfaces are always
static, as are their non-method members.
A class may not have the same simple name as any of its enclosing classes.
this can be qualified, to select one of possibly several current
instances. (Inner classes have two or more current instances.)
The syntax for class instance creation extended to support anonymous classes and enclosing instances:
new TypeName ( ArgumentListopt
new expression may define an anonymous class by specifying its body.
Independently, the type of a
new expression may specified as the simple name
of an inner class, if an instance of the immediately enclosing class is given as a
qualifying expression before the keyword
new. The qualifying instance
becomes the enclosing instance of the new object. A corresponding
super allows a subclass constructor to specify an enclosing
instance for a superclass which is an inner:
If an inner class is constructed by an unqualified
super expression, the
enclosing instance will be the (innermost) current instance of the required type.
Some of the detailed descriptions of name binding in the 1.0 Java Language Specification require amendment to reflect the new regularity in lexical scoping. For example, a simple variable name refers to the innermost lexically apparent definition, whether that definition comes from a class or a block. The same is true for simple type names. The grammar for a qualifier name (i.e., an AmbiguousName) is extended to reflect the possibility of class names qualifying other type names. The initial simple name in a qualified type name is taken to be a class name if a class of that name is in scope; otherwise it is taken to be a package name, as in Java 1.0.
Any inherited member m of a subclass C is in scope within the body of C,
including any inner classes within C. If C itself is an inner class, there may be
definitions of the same kind (variable, method, or type) for m in enclosing
scopes. (The scopes may be blocks, classes, or packages.) In all such cases, the
inherited member m hides the other definitions of m. Additionally, unless the
hidden definition is a package member, the simple name m is illegal; the
programmer must write C
Nested classes of all sorts (top-level or inner) can be imported by either kind of
import statement. Class names in
import statements must be fully package
qualified, and be resolvable without reference to inheritance relations. As in
Java 1.0, it is illegal for a class and a package of the same name to co-exist.
continue statement must refer to a label within the immediately
enclosing method or initializer block. There are no non-local jumps.
The checking of definite assignment includes classes defined by blocks and
expressions, and extends to occurrences of variables within those classes. Any
local variable used but not defined in an inner class must be declared
and must be definitely assigned before the body of the inner class.
Contents | Prev | Next
Inner Classes Specification (HTML generated by dkramer on March 15, 1997)
Copyright © 1996, 1997 Sun Microsystems, Inc. All rights reserved
Please send any comments or corrections to email@example.com