path: root/gcc/java/gcj.texi

@\input texinfo @c -*-texinfo-*-
@setfilename gcj.info
@settitle Guide to GNU gcj

@c Note: When reading this manual you'll find lots of strange
@c circumlocutions like ``compiler for the Java language''.
@c This is necessary due to Sun's restrictions on the use of
@c the word ``Java'.

@c When this manual is copyrighted.
@set copyrights-gcj 2001

@ifinfo
@format
@dircategory Programming
@direntry
* Gcj: (gcj).               Ahead-of-time compiler for the Java language
@end direntry

@dircategory Individual utilities
@direntry
* gcjh: (gcj)Invoking gcjh.
                            Generate header files from Java class files
* jv-scan: (gcj)Invoking jv-scan.
                            Print information about Java source files
* jcf-dump: (gcj)Invoking jcf-dump.
                            Print information about Java class files
* gij: (gcj)Invoking gij.   GNU interpreter for Java bytecode
@end direntry
@end format

Copyright (C) @value{copyrights-gcj} Free Software Foundation, Inc.

Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
are preserved on all copies.

@ignore
Permission is granted to process this file through Tex and print the
results, provided the printed document carries copying permission
notice identical to this one except for the removal of this paragraph
(this paragraph not being relevant to the printed manual).

@end ignore
Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided also that the
sections entitled ``GNU General Public License'' and ``Funding for Free
Software'' are included exactly as in the original, and provided that 
the entire resulting derived work is distributed under the terms of a 
permission notice identical to this one.

Permission is granted to copy and distribute translations of this manual
into another language, under the above conditions for modified versions,
except that the sections entitled ``GNU General Public License'', and
this permission notice, may be included in translations approved by the
Free Software Foundation instead of in the original English.
@end ifinfo

@titlepage
@title GNU gcj
@author Tom Tromey

@page
@vskip 0pt plus 1filll
Copyright @copyright{} @value{copyrights-gcj} Free Software Foundation, Inc.
@sp 2
For the @value{which-g77} Version*
@sp 1
Published by the Free Software Foundation @*
59 Temple Place - Suite 330@*
Boston, MA 02111-1307, USA@*
@sp 1
Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
are preserved on all copies.

Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided also that the
sections entitled ``GNU General Public License,'' ``Funding for Free
Software,'' and ``Protect Your Freedom---Fight `Look And Feel'@w{}'' are
included exactly as in the original, and provided that the entire
resulting derived work is distributed under the terms of a permission
notice identical to this one.

Permission is granted to copy and distribute translations of this manual
into another language, under the above conditions for modified versions,
except that the section entitled ``GNU General Public License,'' and
this permission notice, may be included in translations approved by the
Free Software Foundation instead of in the original English.
@end titlepage
@page


@node Top
@top Introduction

This manual describes how to use @code{gcj}, the GNU compiler for the
Java programming language.  @code{gcj} can generate both @file{.class}
files and object files, and it can read both Java source code and
@file{.class} files.

@menu
* Copying::		The GNU General Public License
* Invoking gcj::	Compiler options supported by @code{gcj}
* Compatibility::	Compatibility between gcj and other tools for Java
* Invoking gcjh::       Generate header files from class files
* Invoking jv-scan::    Print information about source files
* Invoking jcf-dump::   Print information about class files
* Invoking gij::	Interpreting Java bytecodes
* Resources::		Where to look for more information
@end menu


@node Copying
@unnumbered GNU GENERAL PUBLIC LICENSE
@center Version 2, June 1991

@display
Copyright @copyright{} 1989, 1991 Free Software Foundation, Inc.
59 Temple Place - Suite 330, Boston, MA 02111-1307, USA

Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.
@end display

@unnumberedsec Preamble

  The licenses for most software are designed to take away your
freedom to share and change it.  By contrast, the GNU General Public
License is intended to guarantee your freedom to share and change free
software---to make sure the software is free for all its users.  This
General Public License applies to most of the Free Software
Foundation's software and to any other program whose authors commit to
using it.  (Some other Free Software Foundation software is covered by
the GNU Library General Public License instead.)  You can apply it to
your programs, too.

  When we speak of free software, we are referring to freedom, not
price.  Our General Public Licenses are designed to make sure that you
have the freedom to distribute copies of free software (and charge for
this service if you wish), that you receive source code or can get it
if you want it, that you can change the software or use pieces of it
in new free programs; and that you know you can do these things.

  To protect your rights, we need to make restrictions that forbid
anyone to deny you these rights or to ask you to surrender the rights.
These restrictions translate to certain responsibilities for you if you
distribute copies of the software, or if you modify it.

  For example, if you distribute copies of such a program, whether
gratis or for a fee, you must give the recipients all the rights that
you have.  You must make sure that they, too, receive or can get the
source code.  And you must show them these terms so they know their
rights.

  We protect your rights with two steps: (1) copyright the software, and
(2) offer you this license which gives you legal permission to copy,
distribute and/or modify the software.

  Also, for each author's protection and ours, we want to make certain
that everyone understands that there is no warranty for this free
software.  If the software is modified by someone else and passed on, we
want its recipients to know that what they have is not the original, so
that any problems introduced by others will not reflect on the original
authors' reputations.

  Finally, any free program is threatened constantly by software
patents.  We wish to avoid the danger that redistributors of a free
program will individually obtain patent licenses, in effect making the
program proprietary.  To prevent this, we have made it clear that any
patent must be licensed for everyone's free use or not licensed at all.

  The precise terms and conditions for copying, distribution and
modification follow.

@iftex
@unnumberedsec TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
@end iftex
@ifinfo
@center TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
@end ifinfo

@enumerate 0
@item
This License applies to any program or other work which contains
a notice placed by the copyright holder saying it may be distributed
under the terms of this General Public License.  The ``Program'', below,
refers to any such program or work, and a ``work based on the Program''
means either the Program or any derivative work under copyright law:
that is to say, a work containing the Program or a portion of it,
either verbatim or with modifications and/or translated into another
language.  (Hereinafter, translation is included without limitation in
the term ``modification''.)  Each licensee is addressed as ``you''.

Activities other than copying, distribution and modification are not
covered by this License; they are outside its scope.  The act of
running the Program is not restricted, and the output from the Program
is covered only if its contents constitute a work based on the
Program (independent of having been made by running the Program).
Whether that is true depends on what the Program does.

@item
You may copy and distribute verbatim copies of the Program's
source code as you receive it, in any medium, provided that you
conspicuously and appropriately publish on each copy an appropriate
copyright notice and disclaimer of warranty; keep intact all the
notices that refer to this License and to the absence of any warranty;
and give any other recipients of the Program a copy of this License
along with the Program.

You may charge a fee for the physical act of transferring a copy, and
you may at your option offer warranty protection in exchange for a fee.

@item
You may modify your copy or copies of the Program or any portion
of it, thus forming a work based on the Program, and copy and
distribute such modifications or work under the terms of Section 1
above, provided that you also meet all of these conditions:

@enumerate a
@item
You must cause the modified files to carry prominent notices
stating that you changed the files and the date of any change.

@item
You must cause any work that you distribute or publish, that in
whole or in part contains or is derived from the Program or any
part thereof, to be licensed as a whole at no charge to all third
parties under the terms of this License.

@item
If the modified program normally reads commands interactively
when run, you must cause it, when started running for such
interactive use in the most ordinary way, to print or display an
announcement including an appropriate copyright notice and a
notice that there is no warranty (or else, saying that you provide
a warranty) and that users may redistribute the program under
these conditions, and telling the user how to view a copy of this
License.  (Exception: if the Program itself is interactive but
does not normally print such an announcement, your work based on
the Program is not required to print an announcement.)
@end enumerate

These requirements apply to the modified work as a whole.  If
identifiable sections of that work are not derived from the Program,
and can be reasonably considered independent and separate works in
themselves, then this License, and its terms, do not apply to those
sections when you distribute them as separate works.  But when you
distribute the same sections as part of a whole which is a work based
on the Program, the distribution of the whole must be on the terms of
this License, whose permissions for other licensees extend to the
entire whole, and thus to each and every part regardless of who wrote it.

Thus, it is not the intent of this section to claim rights or contest
your rights to work written entirely by you; rather, the intent is to
exercise the right to control the distribution of derivative or
collective works based on the Program.

In addition, mere aggregation of another work not based on the Program
with the Program (or with a work based on the Program) on a volume of
a storage or distribution medium does not bring the other work under
the scope of this License.

@item
You may copy and distribute the Program (or a work based on it,
under Section 2) in object code or executable form under the terms of
Sections 1 and 2 above provided that you also do one of the following:

@enumerate a
@item
Accompany it with the complete corresponding machine-readable
source code, which must be distributed under the terms of Sections
1 and 2 above on a medium customarily used for software interchange; or,

@item
Accompany it with a written offer, valid for at least three
years, to give any third party, for a charge no more than your
cost of physically performing source distribution, a complete
machine-readable copy of the corresponding source code, to be
distributed under the terms of Sections 1 and 2 above on a medium
customarily used for software interchange; or,

@item
Accompany it with the information you received as to the offer
to distribute corresponding source code.  (This alternative is
allowed only for noncommercial distribution and only if you
received the program in object code or executable form with such
an offer, in accord with Subsection b above.)
@end enumerate

The source code for a work means the preferred form of the work for
making modifications to it.  For an executable work, complete source
code means all the source code for all modules it contains, plus any
associated interface definition files, plus the scripts used to
control compilation and installation of the executable.  However, as a
special exception, the source code distributed need not include
anything that is normally distributed (in either source or binary
form) with the major components (compiler, kernel, and so on) of the
operating system on which the executable runs, unless that component
itself accompanies the executable.

If distribution of executable or object code is made by offering
access to copy from a designated place, then offering equivalent
access to copy the source code from the same place counts as
distribution of the source code, even though third parties are not
compelled to copy the source along with the object code.

@item
You may not copy, modify, sublicense, or distribute the Program
except as expressly provided under this License.  Any attempt
otherwise to copy, modify, sublicense or distribute the Program is
void, and will automatically terminate your rights under this License.
However, parties who have received copies, or rights, from you under
this License will not have their licenses terminated so long as such
parties remain in full compliance.

@item
You are not required to accept this License, since you have not
signed it.  However, nothing else grants you permission to modify or
distribute the Program or its derivative works.  These actions are
prohibited by law if you do not accept this License.  Therefore, by
modifying or distributing the Program (or any work based on the
Program), you indicate your acceptance of this License to do so, and
all its terms and conditions for copying, distributing or modifying
the Program or works based on it.

@item
Each time you redistribute the Program (or any work based on the
Program), the recipient automatically receives a license from the
original licensor to copy, distribute or modify the Program subject to
these terms and conditions.  You may not impose any further
restrictions on the recipients' exercise of the rights granted herein.
You are not responsible for enforcing compliance by third parties to
this License.

@item
If, as a consequence of a court judgment or allegation of patent
infringement or for any other reason (not limited to patent issues),
conditions are imposed on you (whether by court order, agreement or
otherwise) that contradict the conditions of this License, they do not
excuse you from the conditions of this License.  If you cannot
distribute so as to satisfy simultaneously your obligations under this
License and any other pertinent obligations, then as a consequence you
may not distribute the Program at all.  For example, if a patent
license would not permit royalty-free redistribution of the Program by
all those who receive copies directly or indirectly through you, then
the only way you could satisfy both it and this License would be to
refrain entirely from distribution of the Program.

If any portion of this section is held invalid or unenforceable under
any particular circumstance, the balance of the section is intended to
apply and the section as a whole is intended to apply in other
circumstances.

It is not the purpose of this section to induce you to infringe any
patents or other property right claims or to contest validity of any
such claims; this section has the sole purpose of protecting the
integrity of the free software distribution system, which is
implemented by public license practices.  Many people have made
generous contributions to the wide range of software distributed
through that system in reliance on consistent application of that
system; it is up to the author/donor to decide if he or she is willing
to distribute software through any other system and a licensee cannot
impose that choice.

This section is intended to make thoroughly clear what is believed to
be a consequence of the rest of this License.

@item
If the distribution and/or use of the Program is restricted in
certain countries either by patents or by copyrighted interfaces, the
original copyright holder who places the Program under this License
may add an explicit geographical distribution limitation excluding
those countries, so that distribution is permitted only in or among
countries not thus excluded.  In such case, this License incorporates
the limitation as if written in the body of this License.

@item
The Free Software Foundation may publish revised and/or new versions
of the General Public License from time to time.  Such new versions will
be similar in spirit to the present version, but may differ in detail to
address new problems or concerns.

Each version is given a distinguishing version number.  If the Program
specifies a version number of this License which applies to it and ``any
later version'', you have the option of following the terms and conditions
either of that version or of any later version published by the Free
Software Foundation.  If the Program does not specify a version number of
this License, you may choose any version ever published by the Free Software
Foundation.

@item
If you wish to incorporate parts of the Program into other free
programs whose distribution conditions are different, write to the author
to ask for permission.  For software which is copyrighted by the Free
Software Foundation, write to the Free Software Foundation; we sometimes
make exceptions for this.  Our decision will be guided by the two goals
of preserving the free status of all derivatives of our free software and
of promoting the sharing and reuse of software generally.

@iftex
@heading NO WARRANTY
@end iftex
@ifinfo
@center NO WARRANTY
@end ifinfo

@item
BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY
FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW.  EXCEPT WHEN
OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES
PROVIDE THE PROGRAM ``AS IS'' WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED
OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.  THE ENTIRE RISK AS
TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU.  SHOULD THE
PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING,
REPAIR OR CORRECTION.

@item
IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR
REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES,
INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING
OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED
TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY
YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER
PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE
POSSIBILITY OF SUCH DAMAGES.
@end enumerate

@iftex
@heading END OF TERMS AND CONDITIONS
@end iftex
@ifinfo
@center END OF TERMS AND CONDITIONS
@end ifinfo

@page
@unnumberedsec How to Apply These Terms to Your New Programs

  If you develop a new program, and you want it to be of the greatest
possible use to the public, the best way to achieve this is to make it
free software which everyone can redistribute and change under these terms.

  To do so, attach the following notices to the program.  It is safest
to attach them to the start of each source file to most effectively
convey the exclusion of warranty; and each file should have at least
the ``copyright'' line and a pointer to where the full notice is found.

@smallexample
@var{one line to give the program's name and a brief idea of what it does.}
Copyright (C) @var{year}  @var{name of author}

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
@end smallexample

Also add information on how to contact you by electronic and paper mail.

If the program is interactive, make it output a short notice like this
when it starts in an interactive mode:

@smallexample
Gnomovision version 69, Copyright (C) @var{year} @var{name of author}
Gnomovision comes with ABSOLUTELY NO WARRANTY; for details
type `show w'.
This is free software, and you are welcome to redistribute it
under certain conditions; type `show c' for details.
@end smallexample

The hypothetical commands @samp{show w} and @samp{show c} should show
the appropriate parts of the General Public License.  Of course, the
commands you use may be called something other than @samp{show w} and
@samp{show c}; they could even be mouse-clicks or menu items---whatever
suits your program.

You should also get your employer (if you work as a programmer) or your
school, if any, to sign a ``copyright disclaimer'' for the program, if
necessary.  Here is a sample; alter the names:

@smallexample
Yoyodyne, Inc., hereby disclaims all copyright interest in the program
`Gnomovision' (which makes passes at compilers) written by James Hacker.

@var{signature of Ty Coon}, 1 April 1989
Ty Coon, President of Vice
@end smallexample

This General Public License does not permit incorporating your program into
proprietary programs.  If your program is a subroutine library, you may
consider it more useful to permit linking proprietary applications with the
library.  If this is what you want to do, use the GNU Library General
Public License instead of this License.


@node Invoking gcj
@chapter Invoking gcj

As @code{gcj} is just another front end to @code{gcc}, it supports many
of the same options as gcc.  @xref{Option Summary, , Option Summary,
gcc, Using the GNU Compiler Collection}.  This manual only documents the
options specific to @code{gcj}.

@menu
* Input and output files::
* Input Options::		How gcj finds files
* Encodings::                   Options controlling source file encoding
* Warnings::			Options controlling warnings specific to gcj
* Code Generation::		Options controlling the output of gcj
* Configure-time Options::	Options you won't use
@end menu

@node Input and output files
@section Input and output files

A @code{gcj} command is like a @code{gcc} command, in that it
consists of a number of options and file names.  The following kinds
of input file names are supported:

@table @code
@item @var{file}.java
Java source files.
@item @var{file}.class
Java bytecode files.
@item @var{file}.zip
@itemx @var{file}.jar
An archive containing one or more @code{.class} files, all of
which are compiled.  The archive may be compressed.
@item @@@var{file}
A file containing a whitespace-separated list of input file names.
(Currently, these must all be @code{.java} source files, but that
may change.)
Each named file is compiled, just as if it had been on the command line.
@item @var{library}.a
@itemx @var{library}.so
@itemx -l@var{libname}
Libraries to use when linking.  See the @code{gcc} manual.
@end table

You can specify more than one input file on the @code{gcj} command line,
in which case they will all be compiled.  If you specify a
@code{-o @var{FILENAME}}
option, all the input files will be compiled together, producing a
single output file, named @var{FILENAME}.
This is allowed even when using @code{-S} or @code{-c},
but not when using @code{-C}.
(This is an extension beyond the what plain @code{gcc} allows.)
(If more than one input file is specified, all must currently
be @code{.java} files, though we hope to fix this.)

@node Input Options
@section Input Options

@cindex class path

@code{gcj} has options to control where it looks to find files it needs.
For instance, @code{gcj} might need to load a class that is referenced
by the file it has been asked to compile.  Like other compilers for the
Java language, @code{gcj} has a notion of a @dfn{class path}.  There are
several options and environment variables which can be used to
manipulate the class path.  When @code{gcj} looks for a given class, it
searches the class path looking for matching @file{.class} or
@file{.java} file.  @code{gcj} comes with a built-in class path which
points at the installed @file{libgcj.jar}, a file which contains all the
standard classes.

In the below, a directory or path component can refer either to an
actual directory on the filesystem, or to a @file{.zip} or @file{.jar}
file, which @code{gcj} will search as if it is a directory.

@table @code
@item -I@var{dir}
All directories specified by @code{-I} are kept in order and prepended
to the class path constructed from all the other options.  Unless
compatibility with tools like @code{javac} is imported, we recommend
always using @code{-I} instead of the other options for manipulating the
class path.

@item --classpath=@var{path}
This sets the class path to @var{path}, a colon-separated list of paths
(on Windows-based systems, a semicolon-separate list of paths).

@item --CLASSPATH=@var{path}
This sets the class path to @var{path}, a colon-separated list of paths
(on Windows-based systems, a semicolon-separate list of paths).  This
differs from the @code{--classpath} option in that it also suppresses
the built-in system path.

@item CLASSPATH
This is an environment variable which holds a list of paths.
@end table

The final class path is constructed like so:

@itemize @bullet
@item
First come all directories specified via @code{-I}.

@item
If @code{--classpath} is specified, its value is appended and processing
stops.  That is, @code{--classpath} suppresses all the options mentioned
later in this list.

@item
If @code{--CLASSPATH} is specified, its value is appended and the
@code{CLASSPATH} environment variable is suppressed.

@item
If the @code{CLASSPATH} environment variable is specified (and was not
suppressed by @code{--CLASSPATH}), then its value is appended.

@item
Finally, the built-in system directory, @file{libgcj.jar}, is appended.
@end itemize

The classfile built by @code{gcj} for the class @code{java.lang.Object}
(and placed in @code{libgcj.jar}) contains a special zero length
attribute @code{gnu.gcj.gcj-compiled}. The compiler looks for this
attribute when loading @code{java.lang.Object} and will report an error
if it isn't found, unless it compiles to bytecode (the option
@code{-fforce-classes-archive-check} can be used to overide this
behavior in this particular case.)

@table @code
@item -fforce-classes-archive-check
This forces the compiler to always check for the special zero length
attribute @code{gnu.gcj.gcj-compiled} in @code{java.lang.Object} and
issue an error if it isn't found.
@end table

@node Encodings
@section Encodings

The Java programming language uses Unicode throughout.  In an effort to
integrate well with other locales, @code{gcj} allows @file{.java} files
to be written using almost any encoding.  @code{gcj} knows how to
convert these encodings into its internal encoding at compile time.

You can use the @code{--encoding=@var{NAME}} option to specify an
encoding (of a particular character set) to use for source files.  If
this is not specified, the default encoding comes from your current
locale.  If your host system has insufficient locale support, then
@code{gcj} assumes the default encoding to be the @samp{UTF-8} encoding
of Unicode.

To implement @code{--encoding}, @code{gcj} simply uses the host
platform's @code{iconv} conversion routine.  This means that in practice
@code{gcj} is limited by the capabilities of the host platform.

The names allowed for the argument @code{--encoding} vary from platform
to platform (since they are not standardized anywhere).  However,
@code{gcj} implements the encoding named @samp{UTF-8} internally, so if
you choose to use this for your source files you can be assured that it
will work on every host.


@node Warnings
@section Warnings

@code{gcj} implements several warnings.  As with other generic
@code{gcc} warnings, if an option of the form @code{-Wfoo} enables a
warning, then @code{-Wno-foo} will disable it.  Here we've chosen to
document the form of the warning which will have an effect -- the
default being the opposite of what is listed.

@table @code
@item -Wredundant-modifiers
With this flag, @code{gcj} will warn about redundant modifiers.  For
instance, it will warn if an interface method is declared @code{public}.

@item -Wextraneous-semicolon
This causes @code{gcj} to warn about empty statements.  Empty statements
have been deprecated.

@item -Wno-out-of-date
This option will cause @code{gcj} not to warn when a source file is
newer than its matching class file.  By default @code{gcj} will warn
about this.

@item -Wunused
This is the same as @code{gcc}'s @code{-Wunused}.

@item -Wall
This is the same as @code{-Wredundant-modifiers -Wextraneous-semicolon
-Wunused}.
@end table


@node Code Generation
@section Code Generation

In addition to the many @code{gcc} options controlling code generation,
@code{gcj} has several options specific to itself.

@table @code
@item --main=@var{CLASSNAME}
This option is used when linking to specify the name of the class whose
@code{main} method should be invoked when the resulting executable is
run.  @footnote{The linker by default looks for a global function named
@code{main}.  Since Java does not have global functions, and a
collection of Java classes may have more than one class with a
@code{main} method, you need to let the linker know which of those
@code{main} methods it should invoke when starting the application.}

@item -D@var{name}[=@var{value}]
This option can only be used with @code{--main}.  It defines a system
property named @var{name} with value @var{value}.  If @var{value} is not
specified then it defaults to the empty string.  These system properties
are initialized at the program's startup and can be retrieved at runtime
using the @code{java.lang.System.getProperty} method.

@item -C
This option is used to tell @code{gcj} to generate bytecode
(@file{.class} files) rather than object code.

@item -d @var{directory}
When used with @code{-C}, this causes all generated @file{.class} files
to be put in the appropriate subdirectory of @var{directory}.  By
default they will be put in subdirectories of the current working
directory.

@item -fno-bounds-check
By default, @code{gcj} generates code which checks the bounds of all
array indexing operations.  With this option, these checks are omitted.
Note that this can result in unpredictable behavior if the code in
question actually does violate array bounds constraints.

@item -fjni
With @code{gcj} there are two options for writing native methods: CNI
and JNI.  By default @code{gcj} assumes you are using CNI.  If you are
compiling a class with native methods, and these methods are implemented
using JNI, then you must use @code{-fjni}.  This option causes
@code{gcj} to generate stubs which will invoke the underlying JNI
methods.
@end table


@node Configure-time Options
@section Configure-time Options

Some @code{gcj} code generations options affect the resulting ABI, and
so can only be meaningfully given when @code{libgcj}, the runtime
package, is configured.  @code{libgcj} puts the appropriate options from
this group into a @samp{spec} file which is read by @code{gcj}.  These
options are listed here for completeness; if you are using @code{libgcj}
then you won't want to touch these options.

@table @code
@item -fuse-boehm-gc
This enables the use of the Boehm GC bitmap marking code.  In particular
this causes @code{gcj} to put an object marking descriptor into each
vtable.

@item -fhash-synchronization
By default, synchronization data (the data used for @code{synchronize},
@code{wait}, and @code{notify}) is pointed to by a word in each object.
With this option @code{gcj} assumes that this information is stored in a
hash table and not in the object itself.

@item -fuse-divide-subroutine
On some systems, a library routine is called to perform integer
division.  This is required to get exception handling correct when
dividing by zero.

@item -fcheck-references
On some systems it's necessary to insert inline checks whenever
accessing an object via a reference.  On other systems you won't need
this because null pointer accesses are caught automatically by the
processor.
@end table


@node Compatibility
@chapter Compatibility with the Java Platform

As we believe it is important that the Java platform not be fragmented,
@code{gcj} and @code{libgcj} try to conform to the relevant Java
specifications.  However, limited manpower and incomplete and unclear
documentation work against us.  So, there are caveats to using
@code{gcj}.

This list of compatibility issues is by no means complete.

@itemize @bullet
@item
@code{gcj} implements the JDK 1.1 language.  It supports inner classes,
though these are known to still be buggy.  It does not yet support the
Java 2 @code{strictfp} keyword (it recognizes the keyword but ignores
it).

@item
@code{libgcj} is largely compatible with the JDK 1.2 libraries.
However, @code{libgcj} is missing many packages, most notably
@code{java.awt}.  There are also individual missing classes and methods.
We currently do not have a list showing differences between
@code{libgcj} and the Java 2 platform.

@item
Sometimes the @code{libgcj} implementation of a method or class differs
from the JDK implementation.  This is not always a bug.  Still, if it
affects you, it probably makes sense to report it so that we can discuss
the appropriate response.
@end itemize


@node Invoking gcjh
@chapter Invoking gcjh

The @code{gcjh} program is used to generate header files from class
files.  It can generate both CNI and JNI header files, as well as stub
implementation files which can be used as a basis for implementing the
required native methods.

@table @code
@item -stubs
This causes @code{gcjh} to generate stub files instead of header files.
By default the stub file will be named after the class, with a suffix of
@samp{.cc}.  In JNI mode, the default output file will have the suffix
@samp{.c}.

@item -jni
This tells @code{gcjh} to generate a JNI header or stub.  By default,
CNI headers are generated.

@item -add @var{text}
Inserts @var{text} into the class body.  This is ignored in JNI mode.

@item -append @var{text}
Inserts @var{text} into the header file after the class declaration.
This is ignored in JNI mode.

@item -friend @var{text}
Inserts @var{text} into the class as a @code{friend} declaration.
This is ignored in JNI mode.

@item -prepend @var{text}
Inserts @var{text} into the header file before the class declaration.
This is ignored in JNI mode.

@item --classpath=@var{path}
@itemx --CLASSPATH=@var{path}
@itemx -I@var{directory}
@itemx -d @var{directory}
@itemx -o @var{file}
These options are all identical to the corresponding @code{gcj} options.

@item -o @var{file}
Sets the output file name.  This cannot be used if there is more than
one class on the command line.

@item -td @var{directory}
Sets the name of the directory to use for temporary files.

@item --help
Print help about @code{gcjh} and exit.  No further processing is done.

@item --version
Print version information for @code{gcjh} and exit.  No further
processing is done.
@end table

All remaining options are considered to be names of classes.


@node Invoking jv-scan
@chapter Invoking jv-scan

The @code{jv-scan} program can be used to print information about a Java
source file (@file{.java} file).

@table @code
@item --complexity
This prints a complexity measure, related to cyclomatic complexity, for
each input file.

@item --encoding=@var{name}
This works like the corresponding @code{gcj} option.

@item --print-main
This prints the name of the class in this file containing a @code{main}
method.

@item --list-class
This lists the names of all classes defined in the input files.

@item --list-filename
If @code{--list-class} is given, this option causes @code{jv-scan} to
also print the name of the file in which each class was found.

@item -o @var{file}
Print output to the named file.
@end table


@node Invoking jcf-dump
@chapter Invoking jcf-dump

This is a class file examiner, similar to @code{javap}.  It will print
information about a number of classes, which are specifed by class name
or file name.

@table @code
@item -c
Disassemble method bodies.  By default method bodies are not printed.

@item --javap
Generate output in @code{javap} format.  The implementation of this
feature is very incomplete.

@item --classpath=@var{path}
@itemx --CLASSPATH=@var{path}
@itemx -I@var{directory}
@itemx -o @var{file}
These options as the same as the corresponding @code{gcj} options.
@end table


@node Invoking gij
@chapter Invoking gij

@code{gij} is a Java bytecode interpreter included with @code{libgcj}.
@code{gij} is not available on every platform; porting it requires a
small amount of assembly programming which has not been done for all the
targets supported by @code{gcj}.

The primary argument to @code{gij} is the name of a class or, with
@code{-jar}, a jar file.  Options before this argument are interpreted
by @code{gij}; remaining options are passed to the interpreted program.

If a class name is specified and this class does not have a @code{main}
method with the appropriate signature (a @code{static void} method with
a @code{String[]} as its sole argument), then @code{gij} will print an
error and exit.

If a jar file is specified then @code{gij} will use information in it to
determine which class' @code{main} method will be invoked.

@code{gij} will invoke the @code{main} method with all the remaining
command-line options.

Note that @code{gij} is not limited to interpreting code.  Because
@code{libgcj} includes a class loader which can dynamically load shared
objects, it is possible to give @code{gij} the name of a class which has
been compiled and put into a shared library on the class path.

@table @code
@item -D@var{name}[=@var{value}]
This defines a system property named @var{name} with value @var{value}.
If @var{value} is not specified then it defaults to the empty string.
These system properties are initialized at the program's startup and can
be retrieved at runtime using the @code{java.lang.System.getProperty}
method.

@item -ms=@var{number}
This sets the initial heap size 

@item -mx=@var{number}
This sets the maximum heap size.

@item -jar
This indicates that the name passed to @code{gij} should be interpreted
as the name of a jar file, not a class.
@end table


@node Resources
@chapter Resources

While writing @code{gcj} and @code{libgcj} we have, of course, relied
heavily on documentation from Sun Microsystems.  In particular we have
used The Java Language Specification (both first and second editions),
the Java Class Libraries (volumes one and two), and the Java Virtual
Machine Specification.  In addition we've used the online documentation
at @uref{http://java.sun.com/}.

The current @code{gcj} home page is
@uref{http://gcc.gnu.org/java/}.

For more information on gcc, see @uref{http://gcc.gnu.org/}.

Some @code{libgcj} testing is done using the Mauve test suite.  This is
a free software Java class library test suite which is being written
because the JCK is not free.  See
@uref{http://sources.redhat.com/mauve/} for more information.

@contents
@bye