Merge from vendor branch LESS:

[dragonfly.git] / contrib / gcc-4.0 / gcc / doc / gcj.info

This is doc/gcj.info, produced by makeinfo version 4.8 from
/scratch/mitchell/gcc-releases/gcc-4.0.1/gcc-4.0.1/gcc/java/gcj.texi.

   Copyright (C) 2001, 2002, 2003, 2004, 2005 Free Software Foundation,
Inc.

   Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.2 or
any later version published by the Free Software Foundation; with the
Invariant Sections being "GNU General Public License", the Front-Cover
texts being (a) (see below), and with the Back-Cover Texts being (b)
(see below).  A copy of the license is included in the section entitled
"GNU Free Documentation License".

   (a) The FSF's Front-Cover Text is:

   A GNU Manual

   (b) The FSF's Back-Cover Text is:

   You have freedom to copy and modify this GNU Manual, like GNU
software.  Copies published by the Free Software Foundation raise
funds for GNU development.

INFO-DIR-SECTION Programming
START-INFO-DIR-ENTRY
* Gcj: (gcj).               Ahead-of-time compiler for the Java language
END-INFO-DIR-ENTRY

INFO-DIR-SECTION Individual utilities
START-INFO-DIR-ENTRY
* gcjh: (gcj)Invoking gcjh.
                            Generate header files from Java class files
* gjnih: (gcj)Invoking gjnih.
                            Generate JNI 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
* gcj-dbtool: (gcj)Invoking gcj-dbtool.
                            Tool for manipulating class file databases.
* jv-convert: (gcj)Invoking jv-convert.
                            Convert file from one encoding to another
* grmic: (gcj)Invoking grmic.
                            Generate stubs for Remote Method Invocation.
* grmiregistry: (gcj)Invoking grmiregistry.
                            The remote object registry.
END-INFO-DIR-ENTRY

   Copyright (C) 2001, 2002, 2003, 2004, 2005 Free Software Foundation,
Inc.

   Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.2 or
any later version published by the Free Software Foundation; with the
Invariant Sections being "GNU General Public License", the Front-Cover
texts being (a) (see below), and with the Back-Cover Texts being (b)
(see below).  A copy of the license is included in the section entitled
"GNU Free Documentation License".

   (a) The FSF's Front-Cover Text is:

   A GNU Manual

   (b) The FSF's Back-Cover Text is:

   You have freedom to copy and modify this GNU Manual, like GNU
software.  Copies published by the Free Software Foundation raise
funds for GNU development.

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Introduction
************

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

* Menu:

* Copying::              The GNU General Public License
* GNU Free Documentation License::
                        How you can share and copy this manual
* Invoking gcj::        Compiler options supported by `gcj'
* Compatibility::       Compatibility between gcj and other tools for Java
* Invoking gcjh::       Generate header files from class files
* Invoking gjnih::      Generate JNI 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
* Invoking gcj-dbtool:: Tool for manipulating class file databases.
* Invoking jv-convert:: Converting from one encoding to another
* Invoking grmic::      Generate stubs for Remote Method Invocation.
* Invoking grmiregistry:: The remote object registry.
* About CNI::           Description of the Compiled Native Interface
* System properties::   Modifying runtime behavior of the libgcj library
* Resources::           Where to look for more information

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GNU GENERAL PUBLIC LICENSE
**************************

                         Version 2, June 1991

     Copyright (C) 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.

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
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   To protect your rights, we need to make restrictions that forbid
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These restrictions translate to certain responsibilities for you if you
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   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
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   We protect your rights with two steps: (1) copyright the software,
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   Also, for each author's protection and ours, we want to make certain
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   Finally, any free program is threatened constantly by software
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   The precise terms and conditions for copying, distribution and
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    TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
  0. 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
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     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
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     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.

  1. 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
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     this License along with the Program.

     You may charge a fee for the physical act of transferring a copy,
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  2. You may modify your copy or copies of the Program or any portion
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     distribute such modifications or work under the terms of Section 1
     above, provided that you also meet all of these conditions:

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

       b. 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.

       c. 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
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          announcement, your work based on the Program is not required
          to print an announcement.)

     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
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     apply to those sections when you distribute them as separate
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     Thus, it is not the intent of this section to claim rights or
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     In addition, mere aggregation of another work not based on the
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  3. 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
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       a. Accompany it with the complete corresponding machine-readable
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  4. You may not copy, modify, sublicense, or distribute the Program
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  5. You are not required to accept this License, since you have not
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  6. Each time you redistribute the Program (or any work based on the
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  7. If, as a consequence of a court judgment or allegation of patent
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     If any portion of this section is held invalid or unenforceable
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     licensee cannot impose that choice.

     This section is intended to make thoroughly clear what is believed
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  8. If the distribution and/or use of the Program is restricted in
     certain countries either by patents or by copyrighted interfaces,
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     License may add an explicit geographical distribution limitation
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  9. The Free Software Foundation may publish revised and/or new
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 10. If you wish to incorporate parts of the Program into other free
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                                NO WARRANTY
 11. 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
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     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.

 12. 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 OF TERMS AND CONDITIONS
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.

     ONE LINE TO GIVE THE PROGRAM'S NAME AND A BRIEF IDEA OF WHAT IT DOES.
     Copyright (C) YEAR  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.

   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:

     Gnomovision version 69, Copyright (C) YEAR 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.

   The hypothetical commands `show w' and `show c' should show the
appropriate parts of the General Public License.  Of course, the
commands you use may be called something other than `show w' and `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:

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

     SIGNATURE OF TY COON, 1 April 1989
     Ty Coon, President of Vice

   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.

\1f
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GNU Free Documentation License
******************************

                      Version 1.2, November 2002

     Copyright (C) 2000,2001,2002 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.

  0. PREAMBLE

     The purpose of this License is to make a manual, textbook, or other
     functional and useful document "free" in the sense of freedom: to
     assure everyone the effective freedom to copy and redistribute it,
     with or without modifying it, either commercially or
     noncommercially.  Secondarily, this License preserves for the
     author and publisher a way to get credit for their work, while not
     being considered responsible for modifications made by others.

     This License is a kind of "copyleft", which means that derivative
     works of the document must themselves be free in the same sense.
     It complements the GNU General Public License, which is a copyleft
     license designed for free software.

     We have designed this License in order to use it for manuals for
     free software, because free software needs free documentation: a
     free program should come with manuals providing the same freedoms
     that the software does.  But this License is not limited to
     software manuals; it can be used for any textual work, regardless
     of subject matter or whether it is published as a printed book.
     We recommend this License principally for works whose purpose is
     instruction or reference.

  1. APPLICABILITY AND DEFINITIONS

     This License applies to any manual or other work, in any medium,
     that contains a notice placed by the copyright holder saying it
     can be distributed under the terms of this License.  Such a notice
     grants a world-wide, royalty-free license, unlimited in duration,
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     A "Modified Version" of the Document means any work containing the
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     A "Secondary Section" is a named appendix or a front-matter section
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     The "Invariant Sections" are certain Secondary Sections whose
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     The Document may include Warranty Disclaimers next to the notice
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     has no effect on the meaning of this License.

  2. VERBATIM COPYING

     You may copy and distribute the Document in any medium, either
     commercially or noncommercially, provided that this License, the
     copyright notices, and the license notice saying this License
     applies to the Document are reproduced in all copies, and that you
     add no other conditions whatsoever to those of this License.  You
     may not use technical measures to obstruct or control the reading
     or further copying of the copies you make or distribute.  However,
     you may accept compensation in exchange for copies.  If you
     distribute a large enough number of copies you must also follow
     the conditions in section 3.

     You may also lend copies, under the same conditions stated above,
     and you may publicly display copies.

  3. COPYING IN QUANTITY

     If you publish printed copies (or copies in media that commonly
     have printed covers) of the Document, numbering more than 100, and
     the Document's license notice requires Cover Texts, you must
     enclose the copies in covers that carry, clearly and legibly, all
     these Cover Texts: Front-Cover Texts on the front cover, and
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     and legibly identify you as the publisher of these copies.  The
     front cover must present the full title with all words of the
     title equally prominent and visible.  You may add other material
     on the covers in addition.  Copying with changes limited to the
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     If the required texts for either cover are too voluminous to fit
     legibly, you should put the first ones listed (as many as fit
     reasonably) on the actual cover, and continue the rest onto
     adjacent pages.

     If you publish or distribute Opaque copies of the Document
     numbering more than 100, you must either include a
     machine-readable Transparent copy along with each Opaque copy, or
     state in or with each Opaque copy a computer-network location from
     which the general network-using public has access to download
     using public-standard network protocols a complete Transparent
     copy of the Document, free of added material.  If you use the
     latter option, you must take reasonably prudent steps, when you
     begin distribution of Opaque copies in quantity, to ensure that
     this Transparent copy will remain thus accessible at the stated
     location until at least one year after the last time you
     distribute an Opaque copy (directly or through your agents or
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     It is requested, but not required, that you contact the authors of
     the Document well before redistributing any large number of
     copies, to give them a chance to provide you with an updated
     version of the Document.

  4. MODIFICATIONS

     You may copy and distribute a Modified Version of the Document
     under the conditions of sections 2 and 3 above, provided that you
     release the Modified Version under precisely this License, with
     the Modified Version filling the role of the Document, thus
     licensing distribution and modification of the Modified Version to
     whoever possesses a copy of it.  In addition, you must do these
     things in the Modified Version:

       A. Use in the Title Page (and on the covers, if any) a title
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       B. List on the Title Page, as authors, one or more persons or
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       C. State on the Title page the name of the publisher of the
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       D. Preserve all the copyright notices of the Document.

       E. Add an appropriate copyright notice for your modifications
          adjacent to the other copyright notices.

       F. Include, immediately after the copyright notices, a license
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       G. Preserve in that license notice the full lists of Invariant
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       H. Include an unaltered copy of this License.

       I. Preserve the section Entitled "History", Preserve its Title,
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       J. Preserve the network location, if any, given in the Document
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       K. For any section Entitled "Acknowledgements" or "Dedications",
          Preserve the Title of the section, and preserve in the
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          acknowledgements and/or dedications given therein.

       L. Preserve all the Invariant Sections of the Document,
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          or the equivalent are not considered part of the section
          titles.

       M. Delete any section Entitled "Endorsements".  Such a section
          may not be included in the Modified Version.

       N. Do not retitle any existing section to be Entitled
          "Endorsements" or to conflict in title with any Invariant
          Section.

       O. Preserve any Warranty Disclaimers.

     If the Modified Version includes new front-matter sections or
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     You may add a section Entitled "Endorsements", provided it contains
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     The author(s) and publisher(s) of the Document do not by this
     License give permission to use their names for publicity for or to
     assert or imply endorsement of any Modified Version.

  5. COMBINING DOCUMENTS

     You may combine the Document with other documents released under
     this License, under the terms defined in section 4 above for
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  6. COLLECTIONS OF DOCUMENTS

     You may make a collection consisting of the Document and other
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     You may extract a single document from such a collection, and
     distribute it individually under this License, provided you insert
     a copy of this License into the extracted document, and follow
     this License in all other respects regarding verbatim copying of
     that document.

  7. AGGREGATION WITH INDEPENDENT WORKS

     A compilation of the Document or its derivatives with other
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     a storage or distribution medium, is called an "aggregate" if the
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     If the Cover Text requirement of section 3 is applicable to these
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     If a section in the Document is Entitled "Acknowledgements",
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     Preserve its Title (section 1) will typically require changing the
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  9. TERMINATION

     You may not copy, modify, sublicense, or distribute the Document
     except as expressly provided for under this License.  Any other
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     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.

 10. FUTURE REVISIONS OF THIS LICENSE

     The Free Software Foundation may publish new, revised versions of
     the GNU Free Documentation 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.  See
     `http://www.gnu.org/copyleft/'.

     Each version of the License is given a distinguishing version
     number.  If the Document specifies that a particular numbered
     version of this License "or any later version" applies to it, you
     have the option of following the terms and conditions either of
     that specified version or of any later version that has been
     published (not as a draft) by the Free Software Foundation.  If
     the Document does not specify a version number of this License,
     you may choose any version ever published (not as a draft) by the
     Free Software Foundation.

ADDENDUM: How to use this License for your documents
====================================================

To use this License in a document you have written, include a copy of
the License in the document and put the following copyright and license
notices just after the title page:

       Copyright (C)  YEAR  YOUR NAME.
       Permission is granted to copy, distribute and/or modify this document
       under the terms of the GNU Free Documentation License, Version 1.2
       or any later version published by the Free Software Foundation;
       with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.
       A copy of the license is included in the section entitled ``GNU
       Free Documentation License''.

   If you have Invariant Sections, Front-Cover Texts and Back-Cover
Texts, replace the "with...Texts." line with this:

         with the Invariant Sections being LIST THEIR TITLES, with
         the Front-Cover Texts being LIST, and with the Back-Cover Texts
         being LIST.

   If you have Invariant Sections without Cover Texts, or some other
combination of the three, merge those two alternatives to suit the
situation.

   If your document contains nontrivial examples of program code, we
recommend releasing these examples in parallel under your choice of
free software license, such as the GNU General Public License, to
permit their use in free software.

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File: gcj.info,  Node: Invoking gcj,  Next: Compatibility,  Prev: GNU Free Documentation License,  Up: Top

1 Invoking gcj
**************

As `gcj' is just another front end to `gcc', it supports many of the
same options as gcc.  *Note Option Summary: (gcc)Option Summary.  This
manual only documents the options specific to `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
* Linking::                     Options for making an executable
* Code Generation::             Options controlling the output of gcj
* Configure-time Options::      Options you won't use

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File: gcj.info,  Node: Input and output files,  Next: Input Options,  Up: Invoking gcj

1.1 Input and output files
==========================

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

`FILE.java'
     Java source files.

`FILE.class'
     Java bytecode files.

`FILE.zip'
`FILE.jar'
     An archive containing one or more `.class' files, all of which are
     compiled.  The archive may be compressed.  Files in an archive
     which don't end with `.class' are treated as resource files; they
     are compiled into the resulting object file as `core:' URLs.

`@FILE'
     A file containing a whitespace-separated list of input file names.
     (Currently, these must all be `.java' source files, but that may
     change.)  Each named file is compiled, just as if it had been on
     the command line.

`LIBRARY.a'
`LIBRARY.so'
`-lLIBNAME'
     Libraries to use when linking.  See the `gcc' manual.

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

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1.2 Input Options
=================

`gcj' has options to control where it looks to find files it needs.
For instance, `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, `gcj' has a notion of a "class path".  There are several
options and environment variables which can be used to manipulate the
class path.  When `gcj' looks for a given class, it searches the class
path looking for matching `.class' or `.java' file.  `gcj' comes with a
built-in class path which points at the installed `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 `.zip' or `.jar' file,
which `gcj' will search as if it is a directory.

`-IDIR'
     All directories specified by `-I' are kept in order and prepended
     to the class path constructed from all the other options.  Unless
     compatibility with tools like `javac' is important, we recommend
     always using `-I' instead of the other options for manipulating the
     class path.

`--classpath=PATH'
     This sets the class path to PATH, a colon-separated list of paths
     (on Windows-based systems, a semicolon-separate list of paths).
     This does not override the builtin ("boot") search path.

`--CLASSPATH=PATH'
     Deprecated synonym for `--classpath'.

`--bootclasspath=PATH'
     Where to find the standard builtin classes, such as
     `java.lang.String'.

`--extdirs=PATH'
     For each directory in the PATH, place the contents of that
     directory at the end of the class path.

`CLASSPATH'
     This is an environment variable which holds a list of paths.

   The final class path is constructed like so:

   * First come all directories specified via `-I'.

   * If `--classpath' is specified, its value is appended.  Otherwise,
     if the `CLASSPATH' environment variable is specified, then its
     value is appended.  Otherwise, the current directory (`"."') is
     appended.

   * If `--bootclasspath' was specified, append its value.  Otherwise,
     append the built-in system directory, `libgcj.jar'.

   * Finally, if `--extdirs' was specified, append the contents of the
     specified directories at the end of the class path.  Otherwise,
     append the contents of the built-in extdirs at
     `$(prefix)/share/java/ext'.

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

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

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1.3 Encodings
=============

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

   You can use the `--encoding=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 `gcj' assumes
the default encoding to be the `UTF-8' encoding of Unicode.

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

   The names allowed for the argument `--encoding' vary from platform
to platform (since they are not standardized anywhere).  However, `gcj'
implements the encoding named `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.

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1.4 Warnings
============

`gcj' implements several warnings.  As with other generic `gcc'
warnings, if an option of the form `-Wfoo' enables a warning, then
`-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.

`-Wredundant-modifiers'
     With this flag, `gcj' will warn about redundant modifiers.  For
     instance, it will warn if an interface method is declared `public'.

`-Wextraneous-semicolon'
     This causes `gcj' to warn about empty statements.  Empty statements
     have been deprecated.

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

`-Wno-deprecated'
     Warn if a deprecated class, method, or field is referred to.

`-Wunused'
     This is the same as `gcc''s `-Wunused'.

`-Wall'
     This is the same as `-Wredundant-modifiers -Wextraneous-semicolon
     -Wunused'.

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File: gcj.info,  Node: Linking,  Next: Code Generation,  Prev: Warnings,  Up: Invoking gcj

1.5 Linking
===========

To turn a Java application into an executable program, you need to link
it with the needed libraries, just as for C or C++.  The linker by
default looks for a global function named `main'.  Since Java does not
have global functions, and a collection of Java classes may have more
than one class with a `main' method, you need to let the linker know
which of those `main' methods it should invoke when starting the
application.  You can do that in any of these ways:

   * Specify the class containing the desired `main' method when you
     link the application, using the `--main' flag, described below.

   * Link the Java package(s) into a shared library (dll) rather than an
     executable.  Then invoke the application using the `gij' program,
     making sure that `gij' can find the libraries it needs.

   * Link the Java packages(s) with the flag `-lgij', which links in
     the `main' routine from the `gij' command.  This allows you to
     select the class whose `main' method you want to run when you run
     the application.  You can also use other `gij' flags, such as `-D'
     flags to set properties.  Using the `-lgij' library (rather than
     the `gij' program of the previous mechanism) has some advantages:
     it is compatible with static linking, and does not require
     configuring or installing libraries.

   These `gij' options relate to linking an executable:

`--main=CLASSNAME'
     This option is used when linking to specify the name of the class
     whose `main' method should be invoked when the resulting
     executable is run.

`-DNAME[=VALUE]'
     This option can only be used with `--main'.  It defines a system
     property named NAME with value VALUE.  If 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 `java.lang.System.getProperty' method.

`-lgij'
     Create an application whose command-line processing is that of the
     `gij' command.

     This option is an alternative to using `--main'; you cannot use
     both.

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1.6 Code Generation
===================

In addition to the many `gcc' options controlling code generation,
`gcj' has several options specific to itself.

`-C'
     This option is used to tell `gcj' to generate bytecode (`.class'
     files) rather than object code.

`--resource RESOURCE-NAME'
     This option is used to tell `gcj' to compile the contents of a
     given file to object code so it may be accessed at runtime with
     the core protocol handler as `core:/RESOURCE-NAME'.  Note that
     RESOURCE-NAME is the name of the resource as found at runtime; for
     instance, it could be used in a call to `ResourceBundle.getBundle'.
     The actual file name to be compiled this way must be specified
     separately.

`-d DIRECTORY'
     When used with `-C', this causes all generated `.class' files to
     be put in the appropriate subdirectory of DIRECTORY.  By default
     they will be put in subdirectories of the current working
     directory.

`-fno-bounds-check'
     By default, `gcj' generates code which checks the bounds of all
     array indexing operations.  With this option, these checks are
     omitted, which can improve performance for code that uses arrays
     extensively.  Note that this can result in unpredictable behavior
     if the code in question actually does violate array bounds
     constraints.  It is safe to use this option if you are sure that
     your code will never throw an `ArrayIndexOutOfBoundsException'.

`-fno-store-check'
     Don't generate array store checks.  When storing objects into
     arrays, a runtime check is normally generated in order to ensure
     that the object is assignment compatible with the component type
     of the array (which may not be known at compile-time).  With this
     option, these checks are omitted.  This can improve performance
     for code which stores objects into arrays frequently.  It is safe
     to use this option if you are sure your code will never throw an
     `ArrayStoreException'.

`-fjni'
     With `gcj' there are two options for writing native methods: CNI
     and JNI.  By default `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 `-fjni'.  This option
     causes `gcj' to generate stubs which will invoke the underlying JNI
     methods.

`-fno-assert'
     Don't recognize the `assert' keyword.  This is for compatibility
     with older versions of the language specification.

`-fno-optimize-static-class-initialization'
     When the optimization level is greater or equal to `-O2', `gcj'
     will try to optimize the way calls into the runtime are made to
     initialize static classes upon their first use (this optimization
     isn't carried out if `-C' was specified.) When compiling to native
     code, `-fno-optimize-static-class-initialization' will turn this
     optimization off, regardless of the optimization level in use.

`--disable-assertions[=CLASS-OR-PACKAGE]'
     Don't include code for checking assertions in the compiled code.
     If `=CLASS-OR-PACKAGE' is missing disables assertion code
     generation for all classes, unless overridden by a more specific
     `--enable-assertions' flag.  If CLASS-OR-PACKAGE is a class name,
     only disables generating assertion checks within the named class
     or its inner classes.  If CLASS-OR-PACKAGE is a package name,
     disables generating assertion checks within the named package or a
     subpackage.

     By default, assertions are enabled when generating class files or
     when not optimizing, and disabled when generating optimized
     binaries.

`--enable-assertions[=CLASS-OR-PACKAGE]'
     Generates code to check assertions.  The option is perhaps
     misnamed, as you still need to turn on assertion checking at
     run-time, and we don't support any easy way to do that.  So this
     flag isn't very useful yet, except to partially override
     `--disable-assertions'.

`-findirect-dispatch'
     `gcj' has a special binary compatibility ABI, which is enabled by
     the `-findirect-dispatch' option.  In this mode, the code
     generated by `gcj' honors the binary compatibility guarantees in
     the Java Language Specification, and the resulting object files do
     not need to be directly linked against their dependencies.
     Instead, all dependencies are looked up at runtime.  This allows
     free mixing of interpreted and compiled code.

     Note that, at present, `-findirect-dispatch' can only be used when
     compiling `.class' files.  It will not work when compiling from
     source.  CNI also does not yet work with the binary compatibility
     ABI.  These restrictions will be lifted in some future release.

     However, if you compile CNI code with the standard ABI, you can
     call it from code built with the binary compatibility ABI.


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File: gcj.info,  Node: Configure-time Options,  Prev: Code Generation,  Up: Invoking gcj

1.7 Configure-time Options
==========================

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

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

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

`-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.

`-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.

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File: gcj.info,  Node: Compatibility,  Next: Invoking gcjh,  Prev: Invoking gcj,  Up: Top

2 Compatibility with the Java Platform
**************************************

As we believe it is important that the Java platform not be fragmented,
`gcj' and `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 `gcj'.

* Menu:

* Limitations::
* Extensions::

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2.1 Standard features not yet supported
=======================================

This list of compatibility issues is by no means complete.

   * `gcj' implements the JDK 1.2 language.  It supports inner classes
     and the new 1.4 `assert' keyword.  It does not yet support the
     Java 2 `strictfp' keyword (it recognizes the keyword but ignores
     it).

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

   * Sometimes the `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.

   * `gcj' does not currently allow for piecemeal replacement of
     components within `libgcj'. Unfortunately, programmers often want
     to use newer versions of certain packages, such as those provided
     by the Apache Software Foundation's Jakarta project.  This has
     forced us to place the `org.w3c.dom' and `org.xml.sax' packages
     into their own libraries, separate from `libgcj'.  If you intend to
     use these classes, you must link them explicitly with
     `-l-org-w3c-dom' and `-l-org-xml-sax'.  Future versions of `gcj'
     may not have this restriction.

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2.2 Extra features unique to gcj
================================

The main feature of `gcj' is that it can compile programs written in
the Java programming language to native code.  Most extensions that
have been added are to facilitate this functionality.

   * `gcj' makes it easy and efficient to mix code written in Java and
     C++.  *Note About CNI::, for more info on how to use this in your
     programs.

   * When you compile your classes into a shared library they can be
     automatically loaded by the `libgcj' system classloader.  When
     trying to load a class `gnu.pkg.SomeClass' the system classloader
     will first try to load the shared library
     `lib-gnu-pkg-SomeClass.so', if that fails to load the class then
     it will try to load `lib-gnu-pkg.so' and finally when the class is
     still not loaded it will try to load `lib-gnu.so'.  Note that all
     `.'s will be transformed into `-'s and that searching for inner
     classes starts with their outermost outer class.  If the class
     cannot be found this way the system classloader tries to use the
     `libgcj' bytecode interpreter to load the class from the standard
     classpath.  This process can be controlled to some degree via the
     `gnu.gcj.runtime.VMClassLoader.library_control' property; *Note
     libgcj Runtime Properties::.

   * `libgcj' includes a special `gcjlib' URL type.  A URL of this form
     is like a `jar' URL, and looks like
     `gcjlib:/path/to/shared/library.so!/path/to/resource'.  An access
     to one of these URLs causes the shared library to be `dlopen()'d,
     and then the resource is looked for in that library.  These URLs
     are most useful when used in conjunction with
     `java.net.URLClassLoader'.  Note that, due to implementation
     limitations, currently any such URL can be accessed by only one
     class loader, and libraries are never unloaded.  This means some
     care must be exercised to make sure that a `gcjlib' URL is not
     accessed by more than one class loader at once.  In a future
     release this limitation will be lifted, and such libraries will be
     mapped privately.

   * A program compiled by `gcj' will examine the `GCJ_PROPERTIES'
     environment variable and change its behavior in some ways.  In
     particular `GCJ_PROPERTIES' holds a list of assignments to global
     properties, such as would be set with the `-D' option to `java'.
     For instance, `java.compiler=gcj' is a valid (but currently
     meaningless) setting.  


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File: gcj.info,  Node: Invoking gcjh,  Next: Invoking gjnih,  Prev: Compatibility,  Up: Top

3 Invoking gcjh
***************

The `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.

`-stubs'
     This causes `gcjh' to generate stub files instead of header files.
     By default the stub file will be named after the class, with a
     suffix of `.cc'.  In JNI mode, the default output file will have
     the suffix `.c'.

`-jni'
     This tells `gcjh' to generate a JNI header or stub.  By default,
     CNI headers are generated.

`-force'
     This option forces `gcjh' to write the output file.

`-old'
     This option is accepted but ignored for compatibility.

`-trace'
     This option is accepted but ignored for compatibility.

`-J OPTION'
     This option is accepted but ignored for compatibility.

`-add TEXT'
     Inserts TEXT into the class body.  This is ignored in JNI mode.

`-append TEXT'
     Inserts TEXT into the header file after the class declaration.
     This is ignored in JNI mode.

`-friend TEXT'
     Inserts TEXT into the class as a `friend' declaration.  This is
     ignored in JNI mode.

`-prepend TEXT'
     Inserts TEXT into the header file before the class declaration.
     This is ignored in JNI mode.

`--classpath=PATH'
`--CLASSPATH=PATH'
`--bootclasspath=PATH'
`-IDIRECTORY'
`-d DIRECTORY'
`-o FILE'
     These options are all identical to the corresponding `gcj' options.

`-o FILE'
     Sets the output file name.  This cannot be used if there is more
     than one class on the command line.

`-td DIRECTORY'
     Sets the name of the directory to use for temporary files.

`-M'
     Print all dependencies to stdout; suppress ordinary output.

`-MM'
     Print non-system dependencies to stdout; suppress ordinary output.

`-MD'
     Print all dependencies to stdout.

`-MMD'
     Print non-system dependencies to stdout.

`--help'
     Print help about `gcjh' and exit.  No further processing is done.

`--version'
     Print version information for `gcjh' and exit.  No further
     processing is done.

`-v, --verbose'
     Print extra information while running.

   All remaining options are considered to be names of classes.

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File: gcj.info,  Node: Invoking gjnih,  Next: Invoking jv-scan,  Prev: Invoking gcjh,  Up: Top

4 Invoking gjnih
****************

The `gjnih' program is used to generate JNI header files from class
files.  Running it is equivalent to running `gcjh -jni'.

`-stubs'
     This causes `gjnih' to generate stub files instead of header files.
     By default the stub file will be named after the class, with a
     suffix of `.c'.

`-jni'
     This option specifies the default behavior which is to generate a
     JNI header or stub.

`-force'
     This option forces `gjnih' to write the output file.

`-old'
     This option is accepted but ignored for compatibility.

`-trace'
     This option is accepted but ignored for compatibility.

`-J OPTION'
     This option is accepted but ignored for compatibility.

`-add TEXT'
     Inserts TEXT into the class body.  This is ignored in by `gjnih'.

`-append TEXT'
     Inserts TEXT into the header file after the class declaration.
     This is ignored in by `gjnih'.

`-friend TEXT'
     Inserts TEXT into the class as a `friend' declaration.  This is
     ignored by `gjnih'.

`-prepend TEXT'
     Inserts TEXT into the header file before the class declaration.
     This is ignored in by `gjnih'.

`--classpath=PATH'
`--CLASSPATH=PATH'
`--bootclasspath=PATH'
`-IDIRECTORY'
`-d DIRECTORY'
`-o FILE'
     These options are all identical to the corresponding `gcj' options.

`-o FILE'
     Sets the output file name.  This cannot be used if there is more
     than one class on the command line.

`-td DIRECTORY'
     Sets the name of the directory to use for temporary files.

`-M'
     Print all dependencies to stdout; suppress ordinary output.

`-MM'
     Print non-system dependencies to stdout; suppress ordinary output.

`-MD'
     Print all dependencies to stdout.

`-MMD'
     Print non-system dependencies to stdout.

`--help'
     Print help about `gjnih' and exit.  No further processing is done.

`--version'
     Print version information for `gjnih' and exit.  No further
     processing is done.

`-v, --verbose'
     Print extra information while running.

   All remaining options are considered to be names of classes.

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File: gcj.info,  Node: Invoking jv-scan,  Next: Invoking jcf-dump,  Prev: Invoking gjnih,  Up: Top

5 Invoking jv-scan
******************

The `jv-scan' program can be used to print information about a Java
source file (`.java' file).

`--no-assert'
     Don't recognize the `assert' keyword, for backwards compatibility
     with older versions of the language specification.

`--complexity'
     This prints a complexity measure, related to cyclomatic
     complexity, for each input file.

`--encoding=NAME'
     This works like the corresponding `gcj' option.

`--print-main'
     This prints the name of the class in this file containing a `main'
     method.

`--list-class'
     This lists the names of all classes defined in the input files.

`--list-filename'
     If `--list-class' is given, this option causes `jv-scan' to also
     print the name of the file in which each class was found.

`-o FILE'
     Print output to the named file.

`--help'
     Print help, then exit.

`--version'
     Print version number, then exit.

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File: gcj.info,  Node: Invoking jcf-dump,  Next: Invoking gij,  Prev: Invoking jv-scan,  Up: Top

6 Invoking jcf-dump
*******************

This is a class file examiner, similar to `javap'.  It will print
information about a number of classes, which are specified by class name
or file name.

`-c'
     Disassemble method bodies.  By default method bodies are not
     printed.

`--print-constants'
     Print the constant pool.  When printing a reference to a constant
     also print its index in the constant pool.

`--javap'
     Generate output in `javap' format.  The implementation of this
     feature is very incomplete.

`--classpath=PATH'
`--CLASSPATH=PATH'
`-IDIRECTORY'
`-o FILE'
     These options as the same as the corresponding `gcj' options.

`--help'
     Print help, then exit.

`--version'
     Print version number, then exit.

`-v, --verbose'
     Print extra information while running.  Implies
     `--print-constants'.

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File: gcj.info,  Node: Invoking gij,  Next: Invoking gcj-dbtool,  Prev: Invoking jcf-dump,  Up: Top

7 Invoking gij
**************

`gij' is a Java bytecode interpreter included with `libgcj'.  `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 `gcj'.

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

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

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

   `gij' will invoke the `main' method with all the remaining
command-line options.

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

`-cp PATH'
`-classpath PATH'
     Set the initial class path.  The class path is used for finding
     class and resource files.  If specified, this option overrides the
     `CLASSPATH' environment variable.  Note that this option is
     ignored if `-jar' is used.

`-DNAME[=VALUE]'
     This defines a system property named NAME with value VALUE.  If
     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
     `java.lang.System.getProperty' method.

`-ms=NUMBER'
     Equivalent to `-Xms'.

`-mx=NUMBER'
     Equivalent to `-Xmx'.

`-noverify'
     Do not verify compliance of bytecode with the VM specification. In
     addition, this option disables type verification which is
     otherwise performed on BC-ABI compiled code.

`-X'
`-XARGUMENT'
     Supplying `-X' by itself will cause `gij' to list all the
     supported `-X' options.  Currently these options are supported:

    `-XmsSIZE'
          Set the initial heap size.

    `-XmxSIZE'
          Set the maximum heap size.

     Unrecognized `-X' options are ignored, for compatibility with
     other runtimes.

`-jar'
     This indicates that the name passed to `gij' should be interpreted
     as the name of a jar file, not a class.

`--help'
`-?'
     Print help, then exit.

`--showversion'
     Print version number and continue.

`--fullversion'
     Print detailed version information, then exit.

`--version'
     Print version number, then exit.

`-verbose'
`-verbose:class'
     Each time a class is initialized, print a short message on
     standard error.

   `gij' also recognizes and ignores the following options, for
compatibility with existing application launch scripts: `-client',
`-server', `-hotspot', `-jrockit', `-agentlib', `-agentpath', `-debug',
`-d32', `-d64', `-javaagent', `-noclassgc', `-verify', and
`-verifyremote'.

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File: gcj.info,  Node: Invoking gcj-dbtool,  Next: Invoking jv-convert,  Prev: Invoking gij,  Up: Top

8 Invoking gcj-dbtool.
**********************

`gcj-dbtool' is a tool for creating and manipulating class file mapping
databases.  `libgcj' can use these databases to find a shared library
corresponding to the bytecode representation of a class.  This
functionality is useful for ahead-of-time compilation of a program that
has no knowledge of `gcj'.

   `gcj-dbtool' works best if all the jar files added to it are
compiled using `-findirect-dispatch'.

   Note that `gcj-dbtool' is currently available as "preview
technology".  We believe it is a reasonable way to allow
application-transparent ahead-of-time compilation, but this is an
unexplored area.  We welcome your comments.

`-n DBFILE [SIZE]'
     This creates a new database.  Currently, databases cannot be
     resized; you can choose a larger initial size if desired.  The
     default size is 32,749.

`-a DBFILE JARFILE LIB'
`-f DBFILE JARFILE LIB'
     This adds a jar file to the database.  For each class file in the
     jar, a cryptographic signature of the bytecode representation of
     the class is recorded in the database.  At runtime, a class is
     looked up by its signature and the compiled form of the class is
     looked for in the corresponding shared library.  The `-a' option
     will verify that LIB exists before adding it to the database; `-f'
     skips this check.

`[`-'][`-0'] -m DBFILE DBFILE,[DBFILE]'
     Merge a number of databases.  The output database overwrites any
     existing database.  To add databases into an existing database,
     include the destination in the list of sources.

     If `-' or `-0' are used, the list of files to read is taken from
     standard input instead of the command line.  For `-0', Input
     filenames are terminated by a null character instead of by
     whitespace.  Useful when arguments might contain white space.  The
     GNU find -print0 option produces input suitable for this mode.

`-t DBFILE'
     Test a database.

`-l DBFILE'
     List the contents of a database.

`-p'
     Print the name of the default database.  If there is no default
     database, this prints a blank line.  If LIBDIR is specified, use
     it instead of the default library directory component of the
     database name.

`--help'
     Print a help message, then exit.

`--version'
`-v'
     Print version information, then exit.


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File: gcj.info,  Node: Invoking jv-convert,  Next: Invoking grmic,  Prev: Invoking gcj-dbtool,  Up: Top

9 Invoking jv-convert
*********************

`jv-convert' [`OPTION'] ... [INPUTFILE [OUTPUTFILE]]

   `jv-convert' is a utility included with `libgcj' which converts a
file from one encoding to another.  It is similar to the Unix `iconv'
utility.

   The encodings supported by `jv-convert' are platform-dependent.
Currently there is no way to get a list of all supported encodings.

`--encoding NAME'
`--from NAME'
     Use NAME as the input encoding.  The default is the current
     locale's encoding.

`--to NAME'
     Use NAME as the output encoding.  The default is the `JavaSrc'
     encoding; this is ASCII with `\u' escapes for non-ASCII characters.

`-i FILE'
     Read from FILE.  The default is to read from standard input.

`-o FILE'
     Write to FILE.  The default is to write to standard output.

`--reverse'
     Swap the input and output encodings.

`--help'
     Print a help message, then exit.

`--version'
     Print version information, then exit.

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File: gcj.info,  Node: Invoking grmic,  Next: Invoking grmiregistry,  Prev: Invoking jv-convert,  Up: Top

10 Invoking grmic
*****************

`grmic' [`OPTION'] ... CLASS ...

   `grmic' is a utility included with `libgcj' which generates stubs
for remote objects.

   Note that this program isn't yet fully compatible with the JDK
`grmic'.  Some options, such as `-classpath', are recognized but
currently ignored.  We have left these options undocumented for now.

   Long options can also be given with a GNU-style leading `--'.  For
instance, `--help' is accepted.

`-keep'
`-keepgenerated'
     By default, `grmic' deletes intermediate files.  Either of these
     options causes it not to delete such files.

`-v1.1'
     Cause `grmic' to create stubs and skeletons for the 1.1 protocol
     version.

`-vcompat'
     Cause `grmic' to create stubs and skeletons compatible with both
     the 1.1 and 1.2 protocol versions.  This is the default.

`-v1.2'
     Cause `grmic' to create stubs and skeletons for the 1.2 protocol
     version.

`-nocompile'
     Don't compile the generated files.

`-verbose'
     Print information about what `grmic' is doing.

`-d DIRECTORY'
     Put output files in DIRECTORY.  By default the files are put in
     the current working directory.

`-help'
     Print a help message, then exit.

`-version'
     Print version information, then exit.

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File: gcj.info,  Node: Invoking grmiregistry,  Next: About CNI,  Prev: Invoking grmic,  Up: Top

11 Invoking grmiregistry
************************

`grmic' [`OPTION'] ... [PORT]

   `grmiregistry' starts a remote object registry on the current host.
If no port number is specified, then port 1099 is used.

`--help'
     Print a help message, then exit.

`--version'
     Print version information, then exit.

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File: gcj.info,  Node: About CNI,  Next: System properties,  Prev: Invoking grmiregistry,  Up: Top

12 About CNI
************

This documents CNI, the Compiled Native Interface, which is is a
convenient way to write Java native methods using C++.  This is a more
efficient, more convenient, but less portable alternative to the
standard JNI (Java Native Interface).

* Menu:

* Basic concepts::              Introduction to using CNI.
* Packages::                    How packages are mapped to C++.
* Primitive types::             Handling Java types in C++.
* Interfaces::                  How Java interfaces map to C++.
* Objects and Classes::         C++ and Java classes.
* Class Initialization::        How objects are initialized.
* Object allocation::           How to create Java objects in C++.
* Memory allocation::           How to allocate and free memory.
* Arrays::                      Dealing with Java arrays in C++.
* Methods::                     Java methods in C++.
* Strings::                     Information about Java Strings.
* Mixing with C++::             How CNI can interoperate with C++.
* Exception Handling::          How exceptions are handled.
* Synchronization::             Synchronizing between Java and C++.
* Invocation::                  Starting the Java runtime from C++.
* Reflection::                  Using reflection from C++.

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File: gcj.info,  Node: Basic concepts,  Next: Packages,  Up: About CNI

12.1 Basic concepts
===================

In terms of languages features, Java is mostly a subset of C++.  Java
has a few important extensions, plus a powerful standard class library,
but on the whole that does not change the basic similarity.  Java is a
hybrid object-oriented language, with a few native types, in addition
to class types.  It is class-based, where a class may have static as
well as per-object fields, and static as well as instance methods.
Non-static methods may be virtual, and may be overloaded.  Overloading
is resolved at compile time by matching the actual argument types
against the parameter types.  Virtual methods are implemented using
indirect calls through a dispatch table (virtual function table).
Objects are allocated on the heap, and initialized using a constructor
method.  Classes are organized in a package hierarchy.

   All of the listed attributes are also true of C++, though C++ has
extra features (for example in C++ objects may be allocated not just on
the heap, but also statically or in a local stack frame).  Because
`gcj' uses the same compiler technology as G++ (the GNU C++ compiler),
it is possible to make the intersection of the two languages use the
same ABI (object representation and calling conventions).  The key idea
in CNI is that Java objects are C++ objects, and all Java classes are
C++ classes (but not the other way around).  So the most important task
in integrating Java and C++ is to remove gratuitous incompatibilities.

   You write CNI code as a regular C++ source file.  (You do have to use
a Java/CNI-aware C++ compiler, specifically a recent version of G++.)

A CNI C++ source file must have:

     #include <gcj/cni.h>

and then must include one header file for each Java class it uses, e.g.:

     #include <java/lang/Character.h>
     #include <java/util/Date.h>
     #include <java/lang/IndexOutOfBoundsException.h>

These header files are automatically generated by `gcjh'.

   CNI provides some functions and macros to make using Java objects and
primitive types from C++ easier.  In general, these CNI functions and
macros start with the `Jv' prefix, for example the function
`JvNewObjectArray'.  This convention is used to avoid conflicts with
other libraries.  Internal functions in CNI start with the prefix
`_Jv_'.  You should not call these; if you find a need to, let us know
and we will try to come up with an alternate solution.

12.1.1 Limitations
------------------

Whilst a Java class is just a C++ class that doesn't mean that you are
freed from the shackles of Java, a CNI C++ class must adhere to the
rules of the Java programming language.

   For example: it is not possible to declare a method in a CNI class
that will take a C string (`char*') as an argument, or to declare a
member variable of some non-Java datatype.

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File: gcj.info,  Node: Packages,  Next: Primitive types,  Prev: Basic concepts,  Up: About CNI

12.2 Packages
=============

The only global names in Java are class names, and packages.  A
"package" can contain zero or more classes, and also zero or more
sub-packages.  Every class belongs to either an unnamed package or a
package that has a hierarchical and globally unique name.

   A Java package is mapped to a C++ "namespace".  The Java class
`java.lang.String' is in the package `java.lang', which is a
sub-package of `java'.  The C++ equivalent is the class
`java::lang::String', which is in the namespace `java::lang' which is
in the namespace `java'.

Here is how you could express this:

     (// Declare the class(es), possibly in a header file:
     namespace java {
       namespace lang {
         class Object;
         class String;
         ...
       }
     }

     class java::lang::String : public java::lang::Object
     {
       ...
     };

The `gcjh' tool automatically generates the necessary namespace
declarations.

12.2.1 Leaving out package names
--------------------------------

Always using the fully-qualified name of a java class can be tiresomely
verbose.  Using the full qualified name also ties the code to a single
package making code changes necessary should the class move from one
package to another.  The Java `package' declaration specifies that the
following class declarations are in the named package, without having
to explicitly name the full package qualifiers.  The `package'
declaration can be followed by zero or more `import' declarations, which
allows either a single class or all the classes in a package to be
named by a simple identifier.  C++ provides something similar with the
`using' declaration and directive.

In Java:

     import PACKAGE-NAME.CLASS-NAME;

allows the program text to refer to CLASS-NAME as a shorthand for the
fully qualified name: `PACKAGE-NAME.CLASS-NAME'.

To achieve the same effect C++, you have to do this:

     using PACKAGE-NAME::CLASS-NAME;

Java can also cause imports on demand, like this:

     import PACKAGE-NAME.*;

Doing this allows any class from the package PACKAGE-NAME to be
referred to only by its class-name within the program text.

The same effect can be achieved in C++ like this:

     using namespace PACKAGE-NAME;

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File: gcj.info,  Node: Primitive types,  Next: Interfaces,  Prev: Packages,  Up: About CNI

12.3 Primitive types
====================

Java provides 8 "primitives" types which represent integers, floats,
characters and booleans (and also the void type).  C++ has its own very
similar concrete types.  Such types in C++ however are not always
implemented in the same way (an int might be 16, 32 or 64 bits for
example) so CNI provides a special C++ type for each primitive Java
type:

*Java type*    *C/C++ typename*   *Description*
`char'         `jchar'            16 bit Unicode character
`boolean'      `jboolean'         logical (true or false) values
`byte'         `jbyte'            8-bit signed integer
`short'        `jshort'           16 bit signed integer
`int'          `jint'             32 bit signed integer
`long'         `jlong'            64 bit signed integer
`float'        `jfloat'           32 bit IEEE floating point number
`double'       `jdouble'          64 bit IEEE floating point number
`void'         `void'             no value

   When referring to a Java type You should always use these C++
typenames (e.g.: `jint') to avoid disappointment.

12.3.1 Reference types associated with primitive types
------------------------------------------------------

In Java each primitive type has an associated reference type, e.g.:
`boolean' has an associated `java.lang.Boolean' class.  In order to
make working with such classes easier GCJ provides the macro
`JvPrimClass':

 -- macro: JvPrimClass type
     Return a pointer to the `Class' object corresponding to the type
     supplied.

          JvPrimClass(void) => java.lang.Void.TYPE


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File: gcj.info,  Node: Interfaces,  Next: Objects and Classes,  Prev: Primitive types,  Up: About CNI

12.4 Interfaces
===============

A Java class can "implement" zero or more "interfaces", in addition to
inheriting from a single base class.

   CNI allows CNI code to implement methods of interfaces.  You can
also call methods through interface references, with some limitations.

   CNI doesn't understand interface inheritance at all yet.  So, you
can only call an interface method when the declared type of the field
being called matches the interface which declares that method.  The
workaround is to cast the interface reference to the right
superinterface.

   For example if you have:

     interface A
     {
       void a();
     }

     interface B extends A
     {
       void b();
     }

   and declare a variable of type `B' in C++, you can't call `a()'
unless you cast it to an `A' first.

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File: gcj.info,  Node: Objects and Classes,  Next: Class Initialization,  Prev: Interfaces,  Up: About CNI

12.5 Objects and Classes
========================

12.5.1 Classes
--------------

All Java classes are derived from `java.lang.Object'.  C++ does not
have a unique root class, but we use the C++ class `java::lang::Object'
as the C++ version of the `java.lang.Object' Java class.  All other
Java classes are mapped into corresponding C++ classes derived from
`java::lang::Object'.

   Interface inheritance (the `implements' keyword) is currently not
reflected in the C++ mapping.

12.5.2 Object fields
--------------------

Each object contains an object header, followed by the instance fields
of the class, in order.  The object header consists of a single pointer
to a dispatch or virtual function table.  (There may be extra fields
_in front of_ the object, for example for memory management, but this
is invisible to the application, and the reference to the object points
to the dispatch table pointer.)

   The fields are laid out in the same order, alignment, and size as in
C++.  Specifically, 8-bite and 16-bit native types (`byte', `short',
`char', and `boolean') are _not_ widened to 32 bits.  Note that the
Java VM does extend 8-bit and 16-bit types to 32 bits when on the VM
stack or temporary registers.

   If you include the `gcjh'-generated header for a class, you can
access fields of Java classes in the _natural_ way.  For example, given
the following Java class:

     public class Int
     {
       public int i;
       public Integer (int i) { this.i = i; }
       public static zero = new Integer(0);
     }

   you can write:

     #include <gcj/cni.h>;
     #include <Int>;

     Int*
     mult (Int *p, jint k)
     {
       if (k == 0)
         return Int::zero;  // Static member access.
       return new Int(p->i * k);
     }

12.5.3 Access specifiers
------------------------

CNI does not strictly enforce the Java access specifiers, because Java
permissions cannot be directly mapped into C++ permission.  Private
Java fields and methods are mapped to private C++ fields and methods,
but other fields and methods are mapped to public fields and methods.

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File: gcj.info,  Node: Class Initialization,  Next: Object allocation,  Prev: Objects and Classes,  Up: About CNI

12.6 Class Initialization
=========================

Java requires that each class be automatically initialized at the time
of the first active use.  Initializing a class involves initializing
the static fields, running code in class initializer methods, and
initializing base classes.  There may also be some implementation
specific actions, such as allocating `String' objects corresponding to
string literals in the code.

   The GCJ compiler inserts calls to `JvInitClass' at appropriate
places to ensure that a class is initialized when required.  The C++
compiler does not insert these calls automatically--it is the
programmer's responsibility to make sure classes are initialized.
However, this is fairly painless because of the conventions assumed by
the Java system.

   First, `libgcj' will make sure a class is initialized before an
instance of that object is created.  This is one of the
responsibilities of the `new' operation.  This is taken care of both in
Java code, and in C++ code.  When G++ sees a `new' of a Java class, it
will call a routine in `libgcj' to allocate the object, and that
routine will take care of initializing the class.  Note however that
this does not happen for Java arrays; you must allocate those using the
appropriate CNI function.  It follows that you can access an instance
field, or call an instance (non-static) method and be safe in the
knowledge that the class and all of its base classes have been
initialized.

   Invoking a static method is also safe.  This is because the Java
compiler adds code to the start of a static method to make sure the
class is initialized.  However, the C++ compiler does not add this
extra code.  Hence, if you write a native static method using CNI, you
are responsible for calling `JvInitClass' before doing anything else in
the method (unless you are sure it is safe to leave it out).

   Accessing a static field also requires the class of the field to be
initialized.  The Java compiler will generate code to call
`Jv_InitClass' before getting or setting the field.  However, the C++
compiler will not generate this extra code, so it is your
responsibility to make sure the class is initialized before you access
a static field from C++.

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File: gcj.info,  Node: Object allocation,  Next: Memory allocation,  Prev: Class Initialization,  Up: About CNI

12.7 Object allocation
======================

New Java objects are allocated using a "class instance creation
expression", e.g.:

     new TYPE ( ... )

   The same syntax is used in C++.  The main difference is that C++
objects have to be explicitly deleted; in Java they are automatically
deleted by the garbage collector.  Using CNI, you can allocate a new
Java object using standard C++ syntax and the C++ compiler will allocate
memory from the garbage collector.  If you have overloaded
constructors, the compiler will choose the correct one using standard
C++ overload resolution rules.

For example:

     java::util::Hashtable *ht = new java::util::Hashtable(120);

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File: gcj.info,  Node: Memory allocation,  Next: Arrays,  Prev: Object allocation,  Up: About CNI

12.8 Memory allocation
======================

When allocting memory in CNI methods it is best to handle out-of-memory
conditions by throwing a Java exception.  These functions are provided
for that purpose:

 -- Function: void* JvMalloc (jsize SIZE)
     Calls malloc.  Throws `java.lang.OutOfMemoryError' if allocation
     fails.

 -- Function: void* JvRealloc (void* PTR, jsize SIZE)
     Calls realloc.  Throws `java.lang.OutOfMemoryError' if
     reallocation fails.

 -- Function: void JvFree (void* PTR)
     Calls free.

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File: gcj.info,  Node: Arrays,  Next: Methods,  Prev: Memory allocation,  Up: About CNI

12.9 Arrays
===========

While in many ways Java is similar to C and C++, it is quite different
in its treatment of arrays.  C arrays are based on the idea of pointer
arithmetic, which would be incompatible with Java's security
requirements.  Java arrays are true objects (array types inherit from
`java.lang.Object').  An array-valued variable is one that contains a
reference (pointer) to an array object.

   Referencing a Java array in C++ code is done using the `JArray'
template, which as defined as follows:

     class __JArray : public java::lang::Object
     {
     public:
       int length;
     };

     template<class T>
     class JArray : public __JArray
     {
       T data[0];
     public:
       T& operator[](jint i) { return data[i]; }
     };

   There are a number of `typedef's which correspond to `typedef's from
the JNI.  Each is the type of an array holding objects of the relevant
type:

     typedef __JArray *jarray;
     typedef JArray<jobject> *jobjectArray;
     typedef JArray<jboolean> *jbooleanArray;
     typedef JArray<jbyte> *jbyteArray;
     typedef JArray<jchar> *jcharArray;
     typedef JArray<jshort> *jshortArray;
     typedef JArray<jint> *jintArray;
     typedef JArray<jlong> *jlongArray;
     typedef JArray<jfloat> *jfloatArray;
     typedef JArray<jdouble> *jdoubleArray;

 -- Method on template<class T>: T* elements (JArray<T> ARRAY)
     This template function can be used to get a pointer to the
     elements of the `array'.  For instance, you can fetch a pointer to
     the integers that make up an `int[]' like so:

          extern jintArray foo;
          jint *intp = elements (foo);

     The name of this function may change in the future.

 -- Function: jobjectArray JvNewObjectArray (jsize LENGTH, jclass
          KLASS, jobject INIT)
     Here `klass' is the type of elements of the array and `init' is
     the initial value put into every slot in the array.

12.9.1 Creating arrays
----------------------

For each primitive type there is a function which can be used to create
a new array of that type.  The name of the function is of the form:

     JvNewTYPEArray

For example:

     JvNewBooleanArray

can be used to create an array of Java primitive boolean types.

The following function definition is the template for all such
functions:

 -- Function: jbooleanArray JvNewBooleanArray (jint LENGTH)
     Create's an array LENGTH indices long.

 -- Function: jsize JvGetArrayLength (jarray ARRAY)
     Returns the length of the ARRAY.

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File: gcj.info,  Node: Methods,  Next: Strings,  Prev: Arrays,  Up: About CNI

12.10 Methods
=============

Java methods are mapped directly into C++ methods.  The header files
generated by `gcjh' include the appropriate method definitions.
Basically, the generated methods have the same names and
_corresponding_ types as the Java methods, and are called in the
natural manner.

12.10.1 Overloading
-------------------

Both Java and C++ provide method overloading, where multiple methods in
a class have the same name, and the correct one is chosen (at compile
time) depending on the argument types.  The rules for choosing the
correct method are (as expected) more complicated in C++ than in Java,
but given a set of overloaded methods generated by `gcjh' the C++
compiler will choose the expected one.

   Common assemblers and linkers are not aware of C++ overloading, so
the standard implementation strategy is to encode the parameter types
of a method into its assembly-level name.  This encoding is called
"mangling", and the encoded name is the "mangled name".  The same
mechanism is used to implement Java overloading.  For C++/Java
interoperability, it is important that both the Java and C++ compilers
use the _same_ encoding scheme.

12.10.2 Static methods
----------------------

Static Java methods are invoked in CNI using the standard C++ syntax,
using the `::' operator rather than the `.' operator.

For example:

     jint i = java::lang::Math::round((jfloat) 2.3);

C++ method definition syntax is used to define a static native method.
For example:

     #include <java/lang/Integer>
     java::lang::Integer*
     java::lang::Integer::getInteger(jstring str)
     {
       ...
     }

12.10.3 Object Constructors
---------------------------

Constructors are called implicitly as part of object allocation using
the `new' operator.

For example:

     java::lang::Integer *x = new java::lang::Integer(234);

   Java does not allow a constructor to be a native method.  This
limitation can be coded round however because a constructor can _call_
a native method.

12.10.4 Instance methods
------------------------

Calling a Java instance method from a C++ CNI method is done using the
standard C++ syntax, e.g.:

     // First create the Java object.
     java::lang::Integer *x = new java::lang::Integer(234);
     // Now call a method.
     jint prim_value = x->intValue();
     if (x->longValue == 0)
       ...

Defining a Java native instance method is also done the natural way:

     #include <java/lang/Integer.h>

     jdouble
     java::lang:Integer::doubleValue()
     {
       return (jdouble) value;
     }

12.10.5 Interface methods
-------------------------

In Java you can call a method using an interface reference.  This is
supported, but not completely.  *Note Interfaces::.

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File: gcj.info,  Node: Strings,  Next: Mixing with C++,  Prev: Methods,  Up: About CNI

12.11 Strings
=============

CNI provides a number of utility functions for working with Java Java
`String' objects.  The names and interfaces are analogous to those of
JNI.

 -- Function: jstring JvNewString (const char* CHARS, jsize LEN)
     Returns a Java `String' object with characters from the C string
     CHARS up to the index LEN in that array.

 -- Function: jstring JvNewStringLatin1 (const char* BYTES, jsize LEN)
     Returns a Java `String' made up of LEN bytes from BYTES.

 -- Function: jstring JvNewStringLatin1 (const char* BYTES)
     As above but the length of the `String' is `strlen(BYTES)'.

 -- Function: jstring JvNewStringUTF (const char* BYTES)
     Returns a `String' which is made up of the UTF encoded characters
     present in the C string BYTES.

 -- Function: jchar* JvGetStringChars (jstring STR)
     Returns a pointer to an array of characters making up the `String'
     STR.

 -- Function: int JvGetStringUTFLength (jstring STR)
     Returns the number of bytes required to encode the contents of the
     `String' STR in UTF-8.

 -- Function: jsize JvGetStringUTFRegion (jstring STR, jsize START,
          jsize LEN, char* BUF)
     Puts the UTF-8 encoding of a region of the `String' STR into the
     buffer `buf'.  The region to fetch is marked by START and LEN.

     Note that BUF is a buffer, not a C string.  It is _not_ null
     terminated.

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File: gcj.info,  Node: Mixing with C++,  Next: Exception Handling,  Prev: Strings,  Up: About CNI

12.12 Interoperating with C/C++
===============================

Because CNI is designed to represent Java classes and methods it cannot
be mixed readily with C/C++ types.

   One important restriction is that Java classes cannot have non-Java
type instance or static variables and cannot have methods which take
non-Java types as arguments or return non-Java types.

None of the following is possible with CNI:


     class ::MyClass : public java::lang::Object
     {
        char* variable;  // char* is not a valid Java type.
     }


     uint
     ::SomeClass::someMethod (char *arg)
     {
       .
       .
       .
     }   // `uint' is not a valid Java type, neither is `char*'

Of course, it is ok to use C/C++ types within the scope of a method:

     jint
     ::SomeClass::otherMethod (jstring str)
     {
        char *arg = ...
        .
        .
        .
     }

12.12.1 RawData
---------------

The above restriction can be problematic, so CNI includes the
`gnu.gcj.RawData' class.  The `RawData' class is a "non-scanned
reference" type.  In other words variables declared of type `RawData'
can contain any data and are not checked by the compiler or memory
manager in any way.

   This means that you can put C/C++ data structures (including classes)
in your CNI classes, as long as you use the appropriate cast.

Here are some examples:


     class ::MyClass : public java::lang::Object
     {
        gnu.gcj.RawData string;

        MyClass ();
        gnu.gcj.RawData getText ();
        void printText ();
     }

     ::MyClass::MyClass ()
     {
        char* text = ...
        string = text;
     }

     gnu.gcj.RawData
     ::MyClass::getText ()
     {
        return string;
     }

     void
     ::MyClass::printText ()
     {
       printf("%s\n", (char*) string);
     }

12.12.2 RawDataManaged
----------------------

`gnu.gcj.RawDataManaged' is another type used to indicate special data
used by native code. Unlike the `RawData' type, fields declared as
`RawDataManaged' will be "marked" by the memory manager and considered
for garbage collection.

   Native data which is allocated using CNI's `JvAllocBytes()' function
and stored in a `RawDataManaged' will be automatically freed when the
Java object it is associated with becomes unreachable.

12.12.3 Native memory allocation
--------------------------------

 -- Function: void* JvAllocBytes (jsize SIZE)
     Allocates SIZE bytes from the heap.  The memory returned is zeroed.
     This memory is not scanned for pointers by the garbage collector,
     but will be freed if no references to it are discovered.

     This function can be useful if you need to associate some native
     data with a Java object. Using a CNI's special `RawDataManaged'
     type, native data allocated with `JvAllocBytes' will be
     automatically freed when the Java object itself becomes
     unreachable.

12.12.4 Posix signals
---------------------

On Posix based systems the `libgcj' library uses several signals
internally.  CNI code should not attempt to use the same signals as
doing so may cause `libgcj' and/or the CNI code to fail.

   SIGSEGV is used on many systems to generate `NullPointerExceptions'.
SIGCHLD is used internally by `Runtime.exec()'.  Several other signals
(that vary from platform to platform) can be used by the memory manager
and by `Thread.interrupt()'.

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File: gcj.info,  Node: Exception Handling,  Next: Synchronization,  Prev: Mixing with C++,  Up: About CNI

12.13 Exception Handling
========================

While C++ and Java share a common exception handling framework, things
are not yet perfectly integrated.  The main issue is that the run-time
type information facilities of the two languages are not integrated.

   Still, things work fairly well.  You can throw a Java exception from
C++ using the ordinary `throw' construct, and this exception can be
caught by Java code.  Similarly, you can catch an exception thrown from
Java using the C++ `catch' construct.

Here is an example:

     if (i >= count)
        throw new java::lang::IndexOutOfBoundsException();

   Normally, G++ will automatically detect when you are writing C++
code that uses Java exceptions, and handle them appropriately.
However, if C++ code only needs to execute destructors when Java
exceptions are thrown through it, GCC will guess incorrectly.  Sample
problematic code:

     struct S { ~S(); };

     extern void bar();    // Is implemented in Java and may throw exceptions.

     void foo()
     {
       S s;
       bar();
     }

   The usual effect of an incorrect guess is a link failure,
complaining of a missing routine called `__gxx_personality_v0'.

   You can inform the compiler that Java exceptions are to be used in a
translation unit, irrespective of what it might think, by writing
`#pragma GCC java_exceptions' at the head of the file.  This `#pragma'
must appear before any functions that throw or catch exceptions, or run
destructors when exceptions are thrown through them.

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File: gcj.info,  Node: Synchronization,  Next: Invocation,  Prev: Exception Handling,  Up: About CNI

12.14 Synchronization
=====================

Each Java object has an implicit monitor.  The Java VM uses the
instruction `monitorenter' to acquire and lock a monitor, and
`monitorexit' to release it.

   The corresponding CNI macros are `JvMonitorEnter' and
`JvMonitorExit' (JNI has similar  methods `MonitorEnter' and
`MonitorExit').

   The Java source language does not provide direct access to these
primitives.  Instead, there is a `synchronized' statement that does an
implicit `monitorenter' before entry to the block, and does a
`monitorexit' on exit from the block.  Note that the lock has to be
released even when the block is abnormally terminated by an exception,
which means there is an implicit `try finally' surrounding
synchronization locks.

   From C++, it makes sense to use a destructor to release a lock.  CNI
defines the following utility class:

     class JvSynchronize() {
       jobject obj;
       JvSynchronize(jobject o) { obj = o; JvMonitorEnter(o); }
       ~JvSynchronize() { JvMonitorExit(obj); }
     };

   So this Java code:

     synchronized (OBJ)
     {
        CODE
     }

might become this C++ code:

     {
        JvSynchronize dummy (OBJ);
        CODE;
     }

   Java also has methods with the `synchronized' attribute.  This is
equivalent to wrapping the entire method body in a `synchronized'
statement.  (Alternatively, an implementation could require the caller
to do the synchronization.  This is not practical for a compiler,
because each virtual method call would have to test at run-time if
synchronization is needed.)  Since in `gcj' the `synchronized'
attribute is handled by the method implementation, it is up to the
programmer of a synchronized native method to handle the synchronization
(in the C++ implementation of the method).  In other words, you need to
manually add `JvSynchronize' in a `native synchronized' method.

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File: gcj.info,  Node: Invocation,  Next: Reflection,  Prev: Synchronization,  Up: About CNI

12.15 Invocation
================

CNI permits C++ applications to make calls into Java classes, in
addition to allowing Java code to call into C++. Several functions,
known as the "invocation API", are provided to support this.

 -- Function: jint JvCreateJavaVM (JvVMInitArgs* VM_ARGS)
     Initializes the Java runtime. This function performs essential
     initialization of the threads interface, garbage collector,
     exception handling and other key aspects of the runtime. It must
     be called once by an application with a non-Java `main()'
     function, before any other Java or CNI calls are made.  It is
     safe, but not recommended, to call `JvCreateJavaVM()' more than
     once provided it is only called from a single thread.  The VMARGS
     parameter can be used to specify initialization parameters for the
     Java runtime. It may be `NULL'.

     JvVMInitArgs represents a list of virtual machine initialization
     arguments. `JvCreateJavaVM()' ignores the version field.

          typedef struct JvVMOption
          {
            // a VM initialization option
            char* optionString;
            // extra information associated with this option
            void* extraInfo;
          } JvVMOption;

          typedef struct JvVMInitArgs
          {
            // for compatibility with JavaVMInitArgs
            jint version;

            // number of VM initialization options
            jint nOptions;

            // an array of VM initialization options
            JvVMOption* options;

            // true if the option parser should ignore unrecognized options
            jboolean ignoreUnrecognized;
          } JvVMInitArgs;

     `JvCreateJavaVM()' returns `0' upon success, or `-1' if the
     runtime is already initialized.

     _Note:_ In GCJ 3.1, the `vm_args' parameter is ignored. It is
     recognized and used as of release 4.0.

 -- Function: java::lang::Thread* JvAttachCurrentThread (jstring NAME,
          java::lang::ThreadGroup* GROUP)
     Registers an existing thread with the Java runtime.  This must be
     called once from each thread, before that thread makes any other
     Java or CNI calls. It must be called after `JvCreateJavaVM'.  NAME
     specifies a name for the thread. It may be `NULL', in which case a
     name will be generated.  GROUP is the ThreadGroup in which this
     thread will be a member. If it is `NULL', the thread will be a
     member of the main thread group.  The return value is the Java
     `Thread' object that represents the thread.  It is safe to call
     `JvAttachCurrentThread()' more than once from the same thread. If
     the thread is already attached, the call is ignored and the current
     thread object is returned.

 -- Function: jint JvDetachCurrentThread ()
     Unregisters a thread from the Java runtime. This should be called
     by threads that were attached using `JvAttachCurrentThread()',
     after they have finished making calls to Java code. This ensures
     that any resources associated with the thread become eligible for
     garbage collection.  This function returns `0' upon success, or
     `-1' if the current thread is not attached.

12.15.1 Handling uncaught exceptions
------------------------------------

If an exception is thrown from Java code called using the invocation
API, and no handler for the exception can be found, the runtime will
abort the application. In order to make the application more robust, it
is recommended that code which uses the invocation API be wrapped by a
top-level try/catch block that catches all Java exceptions.

12.15.2 Example
---------------

The following code demonstrates the use of the invocation API. In this
example, the C++ application initializes the Java runtime and attaches
itself. The `java.lang.System' class is initialized in order to access
its `out' field, and a Java string is printed. Finally, the thread is
detached from the runtime once it has finished making Java calls.
Everything is wrapped with a try/catch block to provide a default
handler for any uncaught exceptions.

   The example can be compiled with `c++ test.cc -lgcj'.

     // test.cc
     #include <gcj/cni.h>
     #include <java/lang/System.h>
     #include <java/io/PrintStream.h>
     #include <java/lang/Throwable.h>

     int main(int argc, char *argv)
     {
       using namespace java::lang;

       try
       {
         JvCreateJavaVM(NULL);
         JvAttachCurrentThread(NULL, NULL);

         String *message = JvNewStringLatin1("Hello from C++");
         JvInitClass(&System::class$);
         System::out->println(message);

         JvDetachCurrentThread();
       }
       catch (Throwable *t)
       {
         System::err->println(JvNewStringLatin1("Unhandled Java exception:"));
         t->printStackTrace();
       }
     }

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File: gcj.info,  Node: Reflection,  Prev: Invocation,  Up: About CNI

12.16 Reflection
================

Reflection is possible with CNI code, it functions similarly to how it
functions with JNI.

   The types `jfieldID' and `jmethodID' are as in JNI.

The functions:

   * `JvFromReflectedField',

   * `JvFromReflectedMethod',

   * `JvToReflectedField'

   * `JvToFromReflectedMethod'

will be added shortly, as will other functions corresponding to JNI.

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File: gcj.info,  Node: System properties,  Next: Resources,  Prev: About CNI,  Up: Top

13 System properties
********************

The runtime behavior of the `libgcj' library can be modified by setting
certain system properties.  These properties can be compiled into the
program using the `-DNAME[=VALUE]' option to `gcj' or by setting them
explicitly in the program by calling the
`java.lang.System.setProperty()' method.  Some system properties are
only used for informational purposes (like giving a version number or a
user name).  A program can inspect the current value of a property by
calling the `java.lang.System.getProperty()' method.

* Menu:

* Standard Properties::         Standard properties supported by `libgcj'
* GNU Classpath Properties::    Properties found in Classpath based libraries
* libgcj Runtime Properties::   Properties specific to `libgcj'

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File: gcj.info,  Node: Standard Properties,  Next: GNU Classpath Properties,  Up: System properties

13.1 Standard Properties
========================

The following properties are normally found in all implementations of
the core libraries for the Java language.

`java.version'
     The `libgcj' version number.

`java.vendor'
     Set to `The Free Software Foundation, Inc.'

`java.vendor.url'
     Set to `http://gcc.gnu.org/java/'.

`java.home'
     The directory where `gcj' was installed.  Taken from the `--prefix'
     option given to `configure'.

`java.class.version'
     The class format version number supported by the libgcj byte code
     interpreter.  (Currently `46.0')

`java.vm.specification.version'
     The Virtual Machine Specification version implemented by `libgcj'.
     (Currently `1.0')

`java.vm.specification.vendor'
     The name of the Virtual Machine specification designer.

`java.vm.specification.name'
     The name of the Virtual Machine specification (Set to `Java
     Virtual Machine Specification').

`java.vm.version'
     The `gcj' version number.

`java.vm.vendor'
     Set to `The Free Software Foundation, Inc.'

`java.vm.name'
     Set to `GNU libgcj'.

`java.specification.version'
     The Runtime Environment specification version implemented by
     `libgcj'.  (Currently set to `1.3')

`java.specification.vendor'
     The Runtime Environment specification designer.

`java.specification.name'
     The name of the Runtime Environment specification (Set to `Java
     Platform API Specification').

`java.class.path'
     The paths (jar files, zip files and directories) used for finding
     class files.

`java.library.path'
     Directory path used for finding native libraries.

`java.io.tmpdir'
     The directory used to put temporary files in.

`java.compiler'
     Name of the Just In Time compiler to use by the byte code
     interpreter.  Currently not used in `libgcj'.

`java.ext.dirs'
     Directories containing jar files with extra libraries.  Will be
     used when resolving classes.

`java.protocol.handler.pkgs'
     A `|' separated list of package names that is used to find classes
     that implement handlers for `java.net.URL'.

`java.rmi.server.codebase'
     A list of URLs that is used by the `java.rmi.server.RMIClassLoader'
     to load classes from.

`jdbc.drivers'
     A list of class names that will be loaded by the
     `java.sql.DriverManager' when it starts up.

`file.separator'
     The separator used in when directories are included in a filename
     (normally `/' or `\' ).

`file.encoding'
     The default character encoding used when converting platform
     native files to Unicode (usually set to `8859_1').

`path.separator'
     The standard separator used when a string contains multiple paths
     (normally `:' or `;'), the string is usually not a valid character
     to use in normal directory names.)

`line.separator'
     The default line separator used on the platform (normally `\n',
     `\r' or a combination of those two characters).

`policy.provider'
     The class name used for the default policy provider returned by
     `java.security.Policy.getPolicy'.

`user.name'
     The name of the user running the program.  Can be the full name,
     the login name or empty if unknown.

`user.home'
     The default directory to put user specific files in.

`user.dir'
     The current working directory from which the program was started.

`user.language'
     The default language as used by the `java.util.Locale' class.

`user.region'
     The default region as used by the `java.util.Local' class.

`user.variant'
     The default variant of the language and region local used.

`user.timezone'
     The default timezone as used by the `java.util.TimeZone' class.

`os.name'
     The operating system/kernel name that the program runs on.

`os.arch'
     The hardware that we are running on.

`os.version'
     The version number of the operating system/kernel.

`awt.appletWarning'
     The string to display when an untrusted applet is displayed.
     Returned by `java.awt.Window.getWarningString()' when the window is
     "insecure".

`awt.toolkit'
     The class name used for initializing the default
     `java.awt.Toolkit'.  Defaults to `gnu.awt.gtk.GtkToolkit'.

`http.proxyHost'
     Name of proxy host for http connections.

`http.proxyPort'
     Port number to use when a proxy host is in use.


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File: gcj.info,  Node: GNU Classpath Properties,  Next: libgcj Runtime Properties,  Prev: Standard Properties,  Up: System properties

13.2 GNU Classpath Properties
=============================

`libgcj' is based on the GNU Classpath (Essential Libraries for Java) a
GNU project to create free core class libraries for use with virtual
machines and compilers for the Java language.  The following properties
are common to libraries based on GNU Classpath.

`gcj.dumpobject'
     Enables printing serialization debugging by the
     `java.io.ObjectInput' and `java.io.ObjectOutput' classes when set
     to something else then the empty string.  Only used when running a
     debug build of the library.

`gnu.classpath.vm.shortname'
     This is a succint name of the virtual machine.  For `libgcj', this
     will always be `libgcj'.

`gnu.classpath.home.url'
     A base URL used for finding system property files (e.g.,
     `classpath.security').  By default this is a `file:' URL pointing
     to the `lib' directory under `java.home'.


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File: gcj.info,  Node: libgcj Runtime Properties,  Prev: GNU Classpath Properties,  Up: System properties

13.3 libgcj Runtime Properties
==============================

The following properties are specific to the `libgcj' runtime and will
normally not be found in other core libraries for the java language.

`java.fullversion'
     The combination of `java.vm.name' and `java.vm.version'.

`java.vm.info'
     Same as `java.fullversion'.

`impl.prefix'
     Used by the `java.net.DatagramSocket' class when set to something
     else then the empty string.  When set all newly created
     `DatagramSocket's will try to load a class
     `java.net.[impl.prefix]DatagramSocketImpl' instead of the normal
     `java.net.PlainDatagramSocketImpl'.

`gnu.gcj.progname'
     The name that was used to invoked the program.

`gnu.gcj.runtime.NameFinder.demangle'
     Whether names in a stack trace should be demangled.  Defaults to
     `true'.

`gnu.gcj.runtime.NameFinder.sanitize'
     Whether calls to initialize exceptions and starting the runtime
     system should be removed from the stack trace.  Only done when
     names are demangled.  Defaults to `true'.

`gnu.gcj.runtime.NameFinder.remove_unknown'
     Whether calls to unknown functions (class and method names are
     unknown) should be removed from the stack trace.  Only done when
     the stack is sanitized.  Ignored if this means no stack trace
     information would be available anymore.  Defaults to `true'.

`gnu.gcj.runtime.NameFinder.remove_interpreter'
     Whether runtime interpreter calls (methods in the
     `_Jv_InterpMethod' class and functions starting with `ffi_')
     should be removed from the stack trace.  Only done when the stack
     is sanitized.  Defaults to `true'.

`gnu.gcj.runtime.NameFinder.use_addr2line'
     Whether an external process (`addr2line' or `addr2name.awk')
     should be used as fallback to convert the addresses to function
     names when the runtime is unable to do it through `dladdr'.

`gnu.gcj.runtime.VMClassLoader.library_control'
     This controls how shared libraries are automatically loaded by the
     built-in class loader.  If this property is set to `full', a full
     search is done for each requested class.  If this property is set
     to `cache' (the default), then any failed lookups are cached and
     not tried again.  If this property is set to `never', then lookups
     are never done.  For more information, *Note Extensions::.

`gnu.gcj.runtime.endorsed.dirs'
     This is like the standard `java.endorsed.dirs', property, but
     specifies some extra directories which are searched after the
     standard endorsed directories.  This is primarily useful for
     telling `libgcj' about additional libraries which are ordinarily
     incorporated into the JDK, and which should be loaded by the
     bootstrap class loader, but which are not yet part of `libgcj'
     itself for some reason.

`gnu.gcj.jit.compiler'
     This is the full path to `gcj' executable which should be used to
     compile classes just-in-time when `ClassLoader.defineClass' is
     called.  If not set, `gcj' will not be invoked by the runtime;
     this can also be controlled via `Compiler.disable'.

`gnu.gcj.jit.options'
     This is a space-separated string of options which should be passed
     to `gcj' when in JIT mode.  If not set, a sensible default is
     chosen.

`gnu.gcj.jit.cachedir'
     This is the directory where cached shared library files are
     stored.  If not set, JIT compilation is disabled.  This should
     never be set to a directory that is writable by any other user.

`gnu.gcj.precompiled.db.path'
     This is a sequence of file names, each referring to a file created
     by `gcj-dbtool'.  These files will be used by `libgcj' to find
     shared libraries corresponding to classes that are loaded from
     bytecode.  `libgcj' often has a built-in default database; it can
     be queried using `gcj-dbtool -p'.


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File: gcj.info,  Node: Resources,  Prev: System properties,  Up: Top

14 Resources
************

While writing `gcj' and `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
`http://java.sun.com/'.

   The current `gcj' home page is `http://gcc.gnu.org/java/'.

   For more information on gcc, see `http://gcc.gnu.org/'.

   Some `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 `http://sources.redhat.com/mauve/'
for more information.


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Tag Table:
Node: Top\7f2837
Node: Copying\7f4128
Node: GNU Free Documentation License\7f23296
Node: Invoking gcj\7f45698
Node: Input and output files\7f46397
Node: Input Options\7f47923
Node: Encodings\7f51071
Node: Warnings\7f52277
Node: Linking\7f53390
Node: Code Generation\7f55623
Node: Configure-time Options\7f60640
Node: Compatibility\7f62063
Node: Limitations\7f62543
Node: Extensions\7f64125
Node: Invoking gcjh\7f66723
Node: Invoking gjnih\7f69078
Node: Invoking jv-scan\7f71266
Node: Invoking jcf-dump\7f72308
Node: Invoking gij\7f73256
Node: Invoking gcj-dbtool\7f76454
Node: Invoking jv-convert\7f78920
Node: Invoking grmic\7f79999
Node: Invoking grmiregistry\7f81389
Node: About CNI\7f81802
Node: Basic concepts\7f83164
Node: Packages\7f86060
Node: Primitive types\7f88388
Node: Interfaces\7f90056
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Node: Object allocation\7f95510
Node: Memory allocation\7f96300
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Node: Mixing with C++\7f103840
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Node: libgcj Runtime Properties\7f122676
Node: Resources\7f126658
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End Tag Table