Java Reference
In-Depth Information
The method
main
must be declared
public
,
static
, and
void
. It must specify a formal parameter
tions is acceptable:
public static void main(String[] args)
public static void main(String... args)
12.2. Loading of Classes and Interfaces
Loading
refers to the process of finding the binary form of a class or interface type with
a particular name, perhaps by computing it on the fly, but more typically by retrieving a
binary representation previously computed from source code by a Java compiler, and con-
structing, from that binary form, a
Class
object to represent the class or interface.
The precise semantics of loading are given in
Chapter 5
of
The Java Virtual Machine Spe-
cification, Java SE 7 Edition
. Here we present an overview of the process from the view-
point of the Java programming language.
The binary format of a class or interface is normally the
class
file format described in
The
Java Virtual Machine Specification, Java SE 7 Edition
cited above, but other formats are
class
ClassLoader
may be used to construct
Class
objects from binary representations in the
class
file format.
Well-behaved class loaders maintain these properties:
• Given the same name, a good class loader should always return the same class ob-
ject.
• If a class loader
L1
delegates loading of a class
C
to another loader
L2
, then for
any type
T
that occurs as the direct superclass or a direct superinterface of
C
, or as
the type of a field in
C
, or as the type of a formal parameter of a method or con-
structor in
C
, or as a return type of a method in
C
,
L1
and
L2
should return the
same
Class
object.
A malicious class loader could violate these properties. However, it could not undermine
the security of the type system, because the Java Virtual Machine guards against this.
For further discussion of these issues, see
The Java Virtual Machine Specification,
Java SE 7 Edition
and the paper
Dynamic Class Loading in the Java Virtual Machine
,
by Sheng Liang and Gilad Bracha, in
Proceedings of OOPSLA '98
, published as
ACM
SIGPLAN Notices
, Volume 33, Number 10, October 1998, pages 36-44. A basic prin-
ciple of the design of the Java programming language is that the run-time type system
