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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.
GNU GENERAL PUBLIC LICENSE The GNU General Public License GNU Free Documentation License How you can share and copy this manual 1. Invoking gcj Compiler options supported by gcj2. Compatibility with the Java Platform Compatibility between gcj and other tools for Java 3. Invoking gcjh Generate header files from class files 4. Invoking jv-scan Print information about source files 5. Invoking jcf-dump Print information about class files 6. Invoking gij Interpreting Java bytecodes 7. Resources Where to look for more information
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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. |
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The licenses for most software are designed to take away your freedom to share and change it. By contrast, the GNU General Public License is intended to guarantee your freedom to share and change free software--to make sure the software is free for all its users. This General Public License applies to most of the Free Software Foundation's software and to any other program whose authors commit to using it. (Some other Free Software Foundation software is covered by the GNU Library General Public License instead.) You can apply it to your programs, too.
When we speak of free software, we are referring to freedom, not price. Our General Public Licenses are designed to make sure that you have the freedom to distribute copies of free software (and charge for this service if you wish), that you receive source code or can get it if you want it, that you can change the software or use pieces of it in new free programs; and that you know you can do these things.
To protect your rights, we need to make restrictions that forbid anyone to deny you these rights or to ask you to surrender the rights. These restrictions translate to certain responsibilities for you if you distribute copies of the software, or if you modify it.
For example, if you distribute copies of such a program, whether gratis or for a fee, you must give the recipients all the rights that you have. You must make sure that they, too, receive or can get the source code. And you must show them these terms so they know their rights.
We protect your rights with two steps: (1) copyright the software, and (2) offer you this license which gives you legal permission to copy, distribute and/or modify the software.
Also, for each author's protection and ours, we want to make certain that everyone understands that there is no warranty for this free software. If the software is modified by someone else and passed on, we want its recipients to know that what they have is not the original, so that any problems introduced by others will not reflect on the original authors' reputations.
Finally, any free program is threatened constantly by software patents. We wish to avoid the danger that redistributors of a free program will individually obtain patent licenses, in effect making the program proprietary. To prevent this, we have made it clear that any patent must be licensed for everyone's free use or not licensed at all.
The precise terms and conditions for copying, distribution and modification follow.
Activities other than copying, distribution and modification are not covered by this License; they are outside its scope. The act of running the Program is not restricted, and the output from the Program is covered only if its contents constitute a work based on the Program (independent of having been made by running the Program). Whether that is true depends on what the Program does.
You may charge a fee for the physical act of transferring a copy, and you may at your option offer warranty protection in exchange for a fee.
These requirements apply to the modified work as a whole. If identifiable sections of that work are not derived from the Program, and can be reasonably considered independent and separate works in themselves, then this License, and its terms, do not apply to those sections when you distribute them as separate works. But when you distribute the same sections as part of a whole which is a work based on the Program, the distribution of the whole must be on the terms of this License, whose permissions for other licensees extend to the entire whole, and thus to each and every part regardless of who wrote it.
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In addition, mere aggregation of another work not based on the Program with the Program (or with a work based on the Program) on a volume of a storage or distribution medium does not bring the other work under the scope of this License.
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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.
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As gcj is just another front end to gcc, it supports many
of the same options as gcc. See section `Option Summary' in Using the GNU Compiler Collection. This manual only documents the
options specific to gcj.
1.1 Input and output files 1.2 Input Options How gcj finds files 1.3 Encodings Options controlling source file encoding 1.4 Warnings Options controlling warnings specific to gcj 1.5 Code Generation Options controlling the output of gcj 1.6 Configure-time Options Options you won't use
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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
file.class
file.zip
file.jar
.class files, all of
which are compiled. The archive may be compressed.
@file
.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
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.
(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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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
-I are kept in order and prepended
to the class path constructed from all the other options. Unless
compatibility with tools like javac is imported, we recommend
always using -I instead of the other options for manipulating the
class path.
--classpath=path
--CLASSPATH=path
--classpath option in that it also suppresses
the built-in system path.
CLASSPATH
The final class path is constructed like so:
-I.
--classpath is specified, its value is appended and processing
stops. That is, --classpath suppresses all the options mentioned
later in this list.
--CLASSPATH is specified, its value is appended and the
CLASSPATH environment variable is suppressed.
CLASSPATH environment variable is specified (and was not
suppressed by --CLASSPATH), then its value is appended.
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 overide this
behavior in this particular case.)
-fforce-classes-archive-check
gnu.gcj.gcj-compiled in java.lang.Object and
issue an error if it isn't found.
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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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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
gcj will warn about redundant modifiers. For
instance, it will warn if an interface method is declared public.
-Wextraneous-semicolon
gcj to warn about empty statements. Empty statements
have been deprecated.
-Wno-out-of-date
gcj not to warn when a source file is
newer than its matching class file. By default gcj will warn
about this.
-Wunused
gcc's -Wunused.
-Wall
-Wredundant-modifiers -Wextraneous-semicolon
-Wunused.
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In addition to the many gcc options controlling code generation,
gcj has several options specific to itself.
--main=CLASSNAME
main method should be invoked when the resulting executable is
run. (1)
-Dname[=value]
--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.
-C
gcj to generate bytecode
(`.class' files) rather than object code.
-d directory
-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
gcj generates code which checks the bounds of all
array indexing operations. With this option, these checks are omitted.
Note that this can result in unpredictable behavior if the code in
question actually does violate array bounds constraints.
-fjni
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.
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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
gcj to put an object marking descriptor into each
vtable.
-fhash-synchronization
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
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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.
This list of compatibility issues is by no means complete.
gcj implements the JDK 1.1 language. It supports inner classes,
though these are known to still be buggy. It does not yet support the
Java 2 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.
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.
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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
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
gcjh to generate a JNI header or stub. By default,
CNI headers are generated.
-add text
-append text
-friend text
friend declaration.
This is ignored in JNI mode.
-prepend text
--classpath=path
--CLASSPATH=path
-Idirectory
-d directory
-o file
gcj options.
-o file
-td directory
--help
gcjh and exit. No further processing is done.
--version
gcjh and exit. No further
processing is done.
All remaining options are considered to be names of classes.
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The jv-scan program can be used to print information about a Java
source file (`.java' file).
--complexity
--encoding=name
gcj option.
--print-main
main
method.
--list-class
--list-filename
--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
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This is a class file examiner, similar to javap. It will print
information about a number of classes, which are specifed by class name
or file name.
-c
--javap
javap format. The implementation of this
feature is very incomplete.
--classpath=path
--CLASSPATH=path
-Idirectory
-o file
gcj options.
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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.
-Dname[=value]
java.lang.System.getProperty
method.
-ms=number
-mx=number
-jar
gij should be interpreted
as the name of a jar file, not a class.
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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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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.
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GNU GENERAL PUBLIC LICENSE
GNU Free Documentation License
1. Invoking gcj
2. Compatibility with the Java Platform
3. Invoking gcjh
4. Invoking jv-scan
5. Invoking jcf-dump
6. Invoking gij
7. Resources
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| Button | Name | Go to | From 1.2.3 go to |
|---|---|---|---|
| [ < ] | Back | previous section in reading order | 1.2.2 |
| [ > ] | Forward | next section in reading order | 1.2.4 |
| [ << ] | FastBack | previous or up-and-previous section | 1.1 |
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| [ >> ] | FastForward | next or up-and-next section | 1.3 |
| [Top] | Top | cover (top) of document | |
| [Contents] | Contents | table of contents | |
| [Index] | Index | concept index | |
| [ ? ] | About | this page |