1 \input texinfo @c -*-texinfo-*-
3 @settitle Guide to GNU gcj
5 @include gcc-common.texi
7 @c Note: When reading this manual you'll find lots of strange
8 @c circumlocutions like ``compiler for the Java language''.
9 @c This is necessary due to Sun's restrictions on the use of
12 @c When this manual is copyrighted.
13 @set copyrights-gcj 2001, 2002, 2003, 2004, 2005
16 @set which-gcj GCC-@value{version-GCC}
19 @c man begin COPYRIGHT
20 Copyright @copyright{} @value{copyrights-gcj} Free Software Foundation, Inc.
22 Permission is granted to copy, distribute and/or modify this document
23 under the terms of the GNU Free Documentation License, Version 1.2 or
24 any later version published by the Free Software Foundation; with the
25 Invariant Sections being ``GNU General Public License'', the Front-Cover
26 texts being (a) (see below), and with the Back-Cover Texts being (b)
27 (see below). A copy of the license is included in the
30 ``GNU Free Documentation License''.
32 @c man begin COPYRIGHT
37 @c man begin COPYRIGHT
39 (a) The FSF's Front-Cover Text is:
43 (b) The FSF's Back-Cover Text is:
45 You have freedom to copy and modify this GNU Manual, like GNU
46 software. Copies published by the Free Software Foundation raise
47 funds for GNU development.
53 @dircategory Programming
55 * Gcj: (gcj). Ahead-of-time compiler for the Java language
58 @dircategory Individual utilities
60 * gcjh: (gcj)Invoking gcjh.
61 Generate header files from Java class files
62 * gjnih: (gcj)Invoking gjnih.
63 Generate JNI header files from Java class files
64 * jv-scan: (gcj)Invoking jv-scan.
65 Print information about Java source files
66 * jcf-dump: (gcj)Invoking jcf-dump.
67 Print information about Java class files
68 * gij: (gcj)Invoking gij. GNU interpreter for Java bytecode
69 * gcj-dbtool: (gcj)Invoking gcj-dbtool.
70 Tool for manipulating class file databases.
71 * jv-convert: (gcj)Invoking jv-convert.
72 Convert file from one encoding to another
73 * grmic: (gcj)Invoking grmic.
74 Generate stubs for Remote Method Invocation.
75 * grmiregistry: (gcj)Invoking grmiregistry.
76 The remote object registry.
88 @vskip 0pt plus 1filll
89 For the @value{which-gcj} Version*
91 Published by the Free Software Foundation @*
92 51 Franklin Street, Fifth Floor@*
93 Boston, MA 02110-1301, USA@*
104 This manual describes how to use @command{gcj}, the GNU compiler for the
105 Java programming language. @command{gcj} can generate both @file{.class}
106 files and object files, and it can read both Java source code and
110 * Copying:: The GNU General Public License
111 * GNU Free Documentation License::
112 How you can share and copy this manual
113 * Invoking gcj:: Compiler options supported by @command{gcj}
114 * Compatibility:: Compatibility between gcj and other tools for Java
115 * Invoking gcjh:: Generate header files from class files
116 * Invoking gjnih:: Generate JNI header files from class files
117 * Invoking jv-scan:: Print information about source files
118 * Invoking jcf-dump:: Print information about class files
119 * Invoking gij:: Interpreting Java bytecodes
120 * Invoking gcj-dbtool:: Tool for manipulating class file databases.
121 * Invoking jv-convert:: Converting from one encoding to another
122 * Invoking grmic:: Generate stubs for Remote Method Invocation.
123 * Invoking grmiregistry:: The remote object registry.
124 * About CNI:: Description of the Compiled Native Interface
125 * System properties:: Modifying runtime behavior of the libgcj library
126 * Resources:: Where to look for more information
136 @chapter Invoking gcj
138 @c man title gcj Ahead-of-time compiler for the Java language
141 @c man begin SYNOPSIS gcj
142 gcj [@option{-I}@var{dir}@dots{}] [@option{-d} @var{dir}@dots{}]
143 [@option{--CLASSPATH}=@var{path}] [@option{--classpath}=@var{path}]
144 [@option{-f}@var{option}@dots{}] [@option{--encoding}=@var{name}]
145 [@option{--main}=@var{classname}] [@option{-D}@var{name}[=@var{value}]@dots{}]
146 [@option{-C}] [@option{--resource} @var{resource-name}] [@option{-d} @var{directory}]
147 [@option{-W}@var{warn}@dots{}]
148 @var{sourcefile}@dots{}
150 @c man begin SEEALSO gcj
151 gcc(1), gcjh(1), gjnih(1), gij(1), jv-scan(1), jcf-dump(1), gfdl(7),
152 and the Info entries for @file{gcj} and @file{gcc}.
156 @c man begin DESCRIPTION gcj
158 As @command{gcj} is just another front end to @command{gcc}, it supports many
159 of the same options as gcc. @xref{Option Summary, , Option Summary,
160 gcc, Using the GNU Compiler Collection (GCC)}. This manual only documents the
161 options specific to @command{gcj}.
166 * Input and output files::
167 * Input Options:: How gcj finds files
168 * Encodings:: Options controlling source file encoding
169 * Warnings:: Options controlling warnings specific to gcj
170 * Linking:: Options for making an executable
171 * Code Generation:: Options controlling the output of gcj
172 * Configure-time Options:: Options you won't use
175 @c man begin OPTIONS gcj
177 @node Input and output files
178 @section Input and output files
180 A @command{gcj} command is like a @command{gcc} command, in that it
181 consists of a number of options and file names. The following kinds
182 of input file names are supported:
185 @item @var{file}.java
187 @item @var{file}.class
190 @itemx @var{file}.jar
191 An archive containing one or more @code{.class} files, all of
192 which are compiled. The archive may be compressed. Files in
193 an archive which don't end with @samp{.class} are treated as
194 resource files; they are compiled into the resulting object file
195 as @samp{core:} URLs.
197 A file containing a whitespace-separated list of input file names.
198 (Currently, these must all be @code{.java} source files, but that
200 Each named file is compiled, just as if it had been on the command line.
201 @item @var{library}.a
202 @itemx @var{library}.so
203 @itemx -l@var{libname}
204 Libraries to use when linking. See the @command{gcc} manual.
207 You can specify more than one input file on the @command{gcj} command line,
208 in which case they will all be compiled. If you specify a
209 @code{-o @var{FILENAME}}
210 option, all the input files will be compiled together, producing a
211 single output file, named @var{FILENAME}.
212 This is allowed even when using @code{-S} or @code{-c},
213 but not when using @code{-C} or @code{--resource}.
214 (This is an extension beyond the what plain @command{gcc} allows.)
215 (If more than one input file is specified, all must currently
216 be @code{.java} files, though we hope to fix this.)
219 @section Input Options
223 @command{gcj} has options to control where it looks to find files it needs.
224 For instance, @command{gcj} might need to load a class that is referenced
225 by the file it has been asked to compile. Like other compilers for the
226 Java language, @command{gcj} has a notion of a @dfn{class path}. There are
227 several options and environment variables which can be used to
228 manipulate the class path. When @command{gcj} looks for a given class, it
229 searches the class path looking for matching @file{.class} or
230 @file{.java} file. @command{gcj} comes with a built-in class path which
231 points at the installed @file{libgcj.jar}, a file which contains all the
234 In the below, a directory or path component can refer either to an
235 actual directory on the filesystem, or to a @file{.zip} or @file{.jar}
236 file, which @command{gcj} will search as if it is a directory.
240 All directories specified by @code{-I} are kept in order and prepended
241 to the class path constructed from all the other options. Unless
242 compatibility with tools like @code{javac} is important, we recommend
243 always using @code{-I} instead of the other options for manipulating the
246 @item --classpath=@var{path}
247 This sets the class path to @var{path}, a colon-separated list of paths
248 (on Windows-based systems, a semicolon-separate list of paths).
249 This does not override the builtin (``boot'') search path.
251 @item --CLASSPATH=@var{path}
252 Deprecated synonym for @code{--classpath}.
254 @item --bootclasspath=@var{path}
255 Where to find the standard builtin classes, such as @code{java.lang.String}.
257 @item --extdirs=@var{path}
258 For each directory in the @var{path}, place the contents of that
259 directory at the end of the class path.
262 This is an environment variable which holds a list of paths.
265 The final class path is constructed like so:
269 First come all directories specified via @code{-I}.
272 If @option{--classpath} is specified, its value is appended.
273 Otherwise, if the @code{CLASSPATH} environment variable is specified,
274 then its value is appended.
275 Otherwise, the current directory (@code{"."}) is appended.
278 If @code{--bootclasspath} was specified, append its value.
279 Otherwise, append the built-in system directory, @file{libgcj.jar}.
282 Finally, if @code{--extdirs} was specified, append the contents of the
283 specified directories at the end of the class path. Otherwise, append
284 the contents of the built-in extdirs at @code{$(prefix)/share/java/ext}.
287 The classfile built by @command{gcj} for the class @code{java.lang.Object}
288 (and placed in @code{libgcj.jar}) contains a special zero length
289 attribute @code{gnu.gcj.gcj-compiled}. The compiler looks for this
290 attribute when loading @code{java.lang.Object} and will report an error
291 if it isn't found, unless it compiles to bytecode (the option
292 @code{-fforce-classes-archive-check} can be used to override this
293 behavior in this particular case.)
296 @item -fforce-classes-archive-check
297 This forces the compiler to always check for the special zero length
298 attribute @code{gnu.gcj.gcj-compiled} in @code{java.lang.Object} and
299 issue an error if it isn't found.
305 The Java programming language uses Unicode throughout. In an effort to
306 integrate well with other locales, @command{gcj} allows @file{.java} files
307 to be written using almost any encoding. @command{gcj} knows how to
308 convert these encodings into its internal encoding at compile time.
310 You can use the @code{--encoding=@var{NAME}} option to specify an
311 encoding (of a particular character set) to use for source files. If
312 this is not specified, the default encoding comes from your current
313 locale. If your host system has insufficient locale support, then
314 @command{gcj} assumes the default encoding to be the @samp{UTF-8} encoding
317 To implement @code{--encoding}, @command{gcj} simply uses the host
318 platform's @code{iconv} conversion routine. This means that in practice
319 @command{gcj} is limited by the capabilities of the host platform.
321 The names allowed for the argument @code{--encoding} vary from platform
322 to platform (since they are not standardized anywhere). However,
323 @command{gcj} implements the encoding named @samp{UTF-8} internally, so if
324 you choose to use this for your source files you can be assured that it
325 will work on every host.
331 @command{gcj} implements several warnings. As with other generic
332 @command{gcc} warnings, if an option of the form @code{-Wfoo} enables a
333 warning, then @code{-Wno-foo} will disable it. Here we've chosen to
334 document the form of the warning which will have an effect -- the
335 default being the opposite of what is listed.
338 @item -Wredundant-modifiers
339 With this flag, @command{gcj} will warn about redundant modifiers. For
340 instance, it will warn if an interface method is declared @code{public}.
342 @item -Wextraneous-semicolon
343 This causes @command{gcj} to warn about empty statements. Empty statements
344 have been deprecated.
346 @item -Wno-out-of-date
347 This option will cause @command{gcj} not to warn when a source file is
348 newer than its matching class file. By default @command{gcj} will warn
351 @item -Wno-deprecated
352 Warn if a deprecated class, method, or field is referred to.
355 This is the same as @command{gcc}'s @code{-Wunused}.
358 This is the same as @code{-Wredundant-modifiers -Wextraneous-semicolon
366 To turn a Java application into an executable program,
367 you need to link it with the needed libraries, just as for C or C++.
368 The linker by default looks for a global function named @code{main}.
369 Since Java does not have global functions, and a
370 collection of Java classes may have more than one class with a
371 @code{main} method, you need to let the linker know which of those
372 @code{main} methods it should invoke when starting the application.
373 You can do that in any of these ways:
377 Specify the class containing the desired @code{main} method
378 when you link the application, using the @code{--main} flag,
381 Link the Java package(s) into a shared library (dll) rather than an
382 executable. Then invoke the application using the @code{gij} program,
383 making sure that @code{gij} can find the libraries it needs.
385 Link the Java packages(s) with the flag @code{-lgij}, which links
386 in the @code{main} routine from the @code{gij} command.
387 This allows you to select the class whose @code{main} method you
388 want to run when you run the application. You can also use
389 other @code{gij} flags, such as @code{-D} flags to set properties.
390 Using the @code{-lgij} library (rather than the @code{gij} program
391 of the previous mechanism) has some advantages: it is compatible with
392 static linking, and does not require configuring or installing libraries.
395 These @code{gij} options relate to linking an executable:
398 @item --main=@var{CLASSNAME}
399 This option is used when linking to specify the name of the class whose
400 @code{main} method should be invoked when the resulting executable is
403 @item -D@var{name}[=@var{value}]
404 This option can only be used with @code{--main}. It defines a system
405 property named @var{name} with value @var{value}. If @var{value} is not
406 specified then it defaults to the empty string. These system properties
407 are initialized at the program's startup and can be retrieved at runtime
408 using the @code{java.lang.System.getProperty} method.
411 Create an application whose command-line processing is that
412 of the @code{gij} command.
414 This option is an alternative to using @code{--main}; you cannot use both.
417 @node Code Generation
418 @section Code Generation
420 In addition to the many @command{gcc} options controlling code generation,
421 @command{gcj} has several options specific to itself.
426 This option is used to tell @command{gcj} to generate bytecode
427 (@file{.class} files) rather than object code.
429 @item --resource @var{resource-name}
430 This option is used to tell @command{gcj} to compile the contents of a
431 given file to object code so it may be accessed at runtime with the core
432 protocol handler as @samp{core:/@var{resource-name}}. Note that
433 @var{resource-name} is the name of the resource as found at runtime; for
434 instance, it could be used in a call to @code{ResourceBundle.getBundle}.
435 The actual file name to be compiled this way must be specified
438 @item -d @var{directory}
439 When used with @code{-C}, this causes all generated @file{.class} files
440 to be put in the appropriate subdirectory of @var{directory}. By
441 default they will be put in subdirectories of the current working
444 @item -fno-bounds-check
445 By default, @command{gcj} generates code which checks the bounds of all
446 array indexing operations. With this option, these checks are omitted, which
447 can improve performance for code that uses arrays extensively. Note that this
448 can result in unpredictable behavior if the code in question actually does
449 violate array bounds constraints. It is safe to use this option if you are
450 sure that your code will never throw an @code{ArrayIndexOutOfBoundsException}.
452 @item -fno-store-check
453 Don't generate array store checks. When storing objects into arrays, a runtime
454 check is normally generated in order to ensure that the object is assignment
455 compatible with the component type of the array (which may not be known
456 at compile-time). With this option, these checks are omitted. This can
457 improve performance for code which stores objects into arrays frequently.
458 It is safe to use this option if you are sure your code will never throw an
459 @code{ArrayStoreException}.
462 With @command{gcj} there are two options for writing native methods: CNI
463 and JNI@. By default @command{gcj} assumes you are using CNI@. If you are
464 compiling a class with native methods, and these methods are implemented
465 using JNI, then you must use @code{-fjni}. This option causes
466 @command{gcj} to generate stubs which will invoke the underlying JNI
470 Don't recognize the @code{assert} keyword. This is for compatibility
471 with older versions of the language specification.
473 @item -fno-optimize-static-class-initialization
474 When the optimization level is greater or equal to @code{-O2},
475 @command{gcj} will try to optimize the way calls into the runtime are made
476 to initialize static classes upon their first use (this optimization
477 isn't carried out if @code{-C} was specified.) When compiling to native
478 code, @code{-fno-optimize-static-class-initialization} will turn this
479 optimization off, regardless of the optimization level in use.
481 @item --disable-assertions[=@var{class-or-package}]
482 Don't include code for checking assertions in the compiled code.
483 If @code{=@var{class-or-package}} is missing disables assertion code
484 generation for all classes, unless overridden by a more
485 specific @code{--enable-assertions} flag.
486 If @var{class-or-package} is a class name, only disables generating
487 assertion checks within the named class or its inner classes.
488 If @var{class-or-package} is a package name, disables generating
489 assertion checks within the named package or a subpackage.
491 By default, assertions are enabled when generating class files
492 or when not optimizing, and disabled when generating optimized binaries.
494 @item --enable-assertions[=@var{class-or-package}]
495 Generates code to check assertions. The option is perhaps misnamed,
496 as you still need to turn on assertion checking at run-time,
497 and we don't support any easy way to do that.
498 So this flag isn't very useful yet, except to partially override
499 @code{--disable-assertions}.
501 @item -findirect-dispatch
502 @command{gcj} has a special binary compatibility ABI, which is enabled
503 by the @code{-findirect-dispatch} option. In this mode, the code
504 generated by @command{gcj} honors the binary compatibility guarantees
505 in the Java Language Specification, and the resulting object files do
506 not need to be directly linked against their dependencies. Instead,
507 all dependencies are looked up at runtime. This allows free mixing of
508 interpreted and compiled code.
510 Note that, at present, @code{-findirect-dispatch} can only be used
511 when compiling @file{.class} files. It will not work when compiling
512 from source. CNI also does not yet work with the binary compatibility
513 ABI. These restrictions will be lifted in some future release.
515 However, if you compile CNI code with the standard ABI, you can call
516 it from code built with the binary compatibility ABI.
518 @item -fbootstrap-classes
519 This option can be use to tell @code{libgcj} that the compiled classes
520 should be loaded by the bootstrap loader, not the system class loader.
521 By default, if you compile a class and link it into an executable, it
522 will be treated as if it was loaded using the system class loader.
523 This is convenient, as it means that things like
524 @code{Class.forName()} will search @samp{CLASSPATH} to find the
530 @node Configure-time Options
531 @section Configure-time Options
533 Some @command{gcj} code generations options affect the resulting ABI, and
534 so can only be meaningfully given when @code{libgcj}, the runtime
535 package, is configured. @code{libgcj} puts the appropriate options from
536 this group into a @samp{spec} file which is read by @command{gcj}. These
537 options are listed here for completeness; if you are using @code{libgcj}
538 then you won't want to touch these options.
542 This enables the use of the Boehm GC bitmap marking code. In particular
543 this causes @command{gcj} to put an object marking descriptor into each
546 @item -fhash-synchronization
547 By default, synchronization data (the data used for @code{synchronize},
548 @code{wait}, and @code{notify}) is pointed to by a word in each object.
549 With this option @command{gcj} assumes that this information is stored in a
550 hash table and not in the object itself.
552 @item -fuse-divide-subroutine
553 On some systems, a library routine is called to perform integer
554 division. This is required to get exception handling correct when
557 @item -fcheck-references
558 On some systems it's necessary to insert inline checks whenever
559 accessing an object via a reference. On other systems you won't need
560 this because null pointer accesses are caught automatically by the
567 @chapter Compatibility with the Java Platform
569 As we believe it is important that the Java platform not be fragmented,
570 @command{gcj} and @code{libgcj} try to conform to the relevant Java
571 specifications. However, limited manpower and incomplete and unclear
572 documentation work against us. So, there are caveats to using
581 @section Standard features not yet supported
583 This list of compatibility issues is by no means complete.
587 @command{gcj} implements the JDK 1.2 language. It supports inner classes
588 and the new 1.4 @code{assert} keyword. It does not yet support the Java 2
589 @code{strictfp} keyword (it recognizes the keyword but ignores it).
592 @code{libgcj} is largely compatible with the JDK 1.2 libraries.
593 However, @code{libgcj} is missing many packages, most notably
594 @code{java.awt}. There are also individual missing classes and methods.
595 We currently do not have a list showing differences between
596 @code{libgcj} and the Java 2 platform.
599 Sometimes the @code{libgcj} implementation of a method or class differs
600 from the JDK implementation. This is not always a bug. Still, if it
601 affects you, it probably makes sense to report it so that we can discuss
602 the appropriate response.
605 @command{gcj} does not currently allow for piecemeal replacement of
606 components within @code{libgcj}. Unfortunately, programmers often want
607 to use newer versions of certain packages, such as those provided by
608 the Apache Software Foundation's Jakarta project. This has forced us
609 to place the @code{org.w3c.dom} and @code{org.xml.sax} packages into
610 their own libraries, separate from @code{libgcj}. If you intend to
611 use these classes, you must link them explicitly with
612 @code{-l-org-w3c-dom} and @code{-l-org-xml-sax}. Future versions of
613 @command{gcj} may not have this restriction.
617 @section Extra features unique to gcj
619 The main feature of @command{gcj} is that it can compile programs written in
620 the Java programming language to native code. Most extensions that have been
621 added are to facilitate this functionality.
625 @command{gcj} makes it easy and efficient to mix code written in Java and C++.
626 @xref{About CNI}, for more info on how to use this in your programs.
629 When you compile your classes into a shared library they can be automatically
630 loaded by the @code{libgcj} system classloader. When trying to load a class
631 @code{gnu.pkg.SomeClass} the system classloader will first try to load the
632 shared library @file{lib-gnu-pkg-SomeClass.so}, if that fails to load the
633 class then it will try to load @file{lib-gnu-pkg.so} and finally when the
634 class is still not loaded it will try to load @file{lib-gnu.so}. Note that
635 all @samp{.}s will be transformed into @samp{-}s and that searching
636 for inner classes starts with their outermost outer class. If the class
637 cannot be found this way the system classloader tries to use
638 the @code{libgcj} bytecode interpreter to load the class from the standard
639 classpath. This process can be controlled to some degree via the
640 @code{gnu.gcj.runtime.VMClassLoader.library_control} property;
641 @xref{libgcj Runtime Properties}.
644 @code{libgcj} includes a special @samp{gcjlib} URL type. A URL of
645 this form is like a @code{jar} URL, and looks like
646 @samp{gcjlib:/path/to/shared/library.so!/path/to/resource}. An access
647 to one of these URLs causes the shared library to be @code{dlopen()}d,
648 and then the resource is looked for in that library. These URLs are
649 most useful when used in conjunction with @code{java.net.URLClassLoader}.
650 Note that, due to implementation limitations, currently any such URL
651 can be accessed by only one class loader, and libraries are never
652 unloaded. This means some care must be exercised to make sure that
653 a @code{gcjlib} URL is not accessed by more than one class loader at once.
654 In a future release this limitation will be lifted, and such
655 libraries will be mapped privately.
658 A program compiled by @command{gcj} will examine the
659 @env{GCJ_PROPERTIES} environment variable and change its behavior in
660 some ways. In particular @env{GCJ_PROPERTIES} holds a list of
661 assignments to global properties, such as would be set with the
662 @option{-D} option to @command{java}. For instance,
663 @samp{java.compiler=gcj} is a valid (but currently meaningless)
665 @cindex GCJ_PROPERTIES
666 @vindex GCJ_PROPERTIES
672 @chapter Invoking gcjh
674 @c man title gcjh generate header files from Java class files
676 @c man begin DESCRIPTION gcjh
678 The @code{gcjh} program is used to generate header files from class
679 files. It can generate both CNI and JNI header files, as well as stub
680 implementation files which can be used as a basis for implementing the
681 required native methods.
686 @c man begin SYNOPSIS gcjh
687 gcjh [@option{-stubs}] [@option{-jni}]
688 [@option{-force}] [@option{-old}] [@option{-trace}] [@option{-J} @var{option}]
689 [@option{-add} @var{text}] [@option{-append} @var{text}] [@option{-friend} @var{text}]
690 [@option{-preprend} @var{text}]
691 [@option{--classpath}=@var{path}] [@option{--CLASSPATH}=@var{path}]
692 [@option{--bootclasspath}=@var{path}]
693 [@option{-I}@var{dir}@dots{}] [@option{-d} @var{dir}@dots{}]
694 [@option{-o} @var{file}] [@option{-td} @var{dir}]
695 [@option{-M}] [@option{-MM}] [@option{-MD}] [@option{-MMD}]
696 [@option{--version}] [@option{--help}] [@option{-v}] [@option{--verbose}]
697 @var{classname}@dots{}
699 @c man begin SEEALSO gcjh
700 gcc(1), gcj(1), gij(1), jv-scan(1), jcf-dump(1), gfdl(7),
701 and the Info entries for @file{gcj} and @file{gcc}.
705 @c man begin OPTIONS gcjh
709 This causes @code{gcjh} to generate stub files instead of header files.
710 By default the stub file will be named after the class, with a suffix of
711 @samp{.cc}. In JNI mode, the default output file will have the suffix
715 This tells @code{gcjh} to generate a JNI header or stub. By default,
716 CNI headers are generated.
719 This option forces @code{gcjh} to write the output file.
722 This option is accepted but ignored for compatibility.
725 This option is accepted but ignored for compatibility.
727 @item -J @var{option}
728 This option is accepted but ignored for compatibility.
730 @item -add @var{text}
731 Inserts @var{text} into the class body. This is ignored in JNI mode.
733 @item -append @var{text}
734 Inserts @var{text} into the header file after the class declaration.
735 This is ignored in JNI mode.
737 @item -friend @var{text}
738 Inserts @var{text} into the class as a @code{friend} declaration.
739 This is ignored in JNI mode.
741 @item -prepend @var{text}
742 Inserts @var{text} into the header file before the class declaration.
743 This is ignored in JNI mode.
745 @item --classpath=@var{path}
746 @itemx --CLASSPATH=@var{path}
747 @itemx --bootclasspath=@var{path}
748 @itemx -I@var{directory}
749 @itemx -d @var{directory}
751 These options are all identical to the corresponding @command{gcj} options.
754 Sets the output file name. This cannot be used if there is more than
755 one class on the command line.
757 @item -td @var{directory}
758 Sets the name of the directory to use for temporary files.
761 Print all dependencies to stdout; suppress ordinary output.
764 Print non-system dependencies to stdout; suppress ordinary output.
767 Print all dependencies to stdout.
770 Print non-system dependencies to stdout.
773 Print help about @code{gcjh} and exit. No further processing is done.
776 Print version information for @code{gcjh} and exit. No further
780 Print extra information while running.
783 All remaining options are considered to be names of classes.
788 @chapter Invoking gjnih
790 @c man title gjnih generate JNI header files from Java class files
792 @c man begin DESCRIPTION gjnih
794 The @code{gjnih} program is used to generate JNI header files from class
795 files. Running it is equivalent to running @code{gcjh -jni}.
800 @c man begin SYNOPSIS gjnih
801 gjnih [@option{-stubs}] [@option{-jni}]
802 [@option{-force}] [@option{-old}] [@option{-trace}] [@option{-J} @var{option}]
803 [@option{-add} @var{text}] [@option{-append} @var{text}] [@option{-friend} @var{text}]
804 [@option{-preprend} @var{text}]
805 [@option{--classpath}=@var{path}] [@option{--CLASSPATH}=@var{path}]
806 [@option{--bootclasspath}=@var{path}]
807 [@option{-I}@var{dir}@dots{}] [@option{-d} @var{dir}@dots{}]
808 [@option{-o} @var{file}] [@option{-td} @var{dir}]
809 [@option{-M}] [@option{-MM}] [@option{-MD}] [@option{-MMD}]
810 [@option{--version}] [@option{--help}] [@option{-v}] [@option{--verbose}]
811 @var{classname}@dots{}
813 @c man begin SEEALSO gjnih
814 gcc(1), gcj(1), gcjh(1), gij(1), jv-scan(1), jcf-dump(1), gfdl(7),
815 and the Info entries for @file{gcj} and @file{gcc}.
819 @c man begin OPTIONS gjnih
823 This causes @code{gjnih} to generate stub files instead of header files.
824 By default the stub file will be named after the class, with a suffix of
828 This option specifies the default behavior which is to generate a JNI
832 This option forces @code{gjnih} to write the output file.
835 This option is accepted but ignored for compatibility.
838 This option is accepted but ignored for compatibility.
840 @item -J @var{option}
841 This option is accepted but ignored for compatibility.
843 @item -add @var{text}
844 Inserts @var{text} into the class body. This is ignored in by
847 @item -append @var{text}
848 Inserts @var{text} into the header file after the class declaration.
849 This is ignored in by @code{gjnih}.
851 @item -friend @var{text}
852 Inserts @var{text} into the class as a @code{friend} declaration.
853 This is ignored by @code{gjnih}.
855 @item -prepend @var{text}
856 Inserts @var{text} into the header file before the class declaration.
857 This is ignored in by @code{gjnih}.
859 @item --classpath=@var{path}
860 @itemx --CLASSPATH=@var{path}
861 @itemx --bootclasspath=@var{path}
862 @itemx -I@var{directory}
863 @itemx -d @var{directory}
865 These options are all identical to the corresponding @command{gcj} options.
868 Sets the output file name. This cannot be used if there is more than
869 one class on the command line.
871 @item -td @var{directory}
872 Sets the name of the directory to use for temporary files.
875 Print all dependencies to stdout; suppress ordinary output.
878 Print non-system dependencies to stdout; suppress ordinary output.
881 Print all dependencies to stdout.
884 Print non-system dependencies to stdout.
887 Print help about @code{gjnih} and exit. No further processing is done.
890 Print version information for @code{gjnih} and exit. No further
894 Print extra information while running.
897 All remaining options are considered to be names of classes.
901 @node Invoking jv-scan
902 @chapter Invoking jv-scan
904 @c man title jv-scan print information about Java source file
906 @c man begin DESCRIPTION jv-scan
908 The @code{jv-scan} program can be used to print information about a Java
909 source file (@file{.java} file).
914 @c man begin SYNOPSIS jv-scan
915 jv-scan [@option{--no-assert}] [@option{--complexity}]
916 [@option{--encoding}=@var{name}] [@option{--print-main}]
917 [@option{--list-class}] [@option{--list-filename}]
918 [@option{--version}] [@option{--help}]
919 [@option{-o} @var{file}] @var{inputfile}@dots{}
921 @c man begin SEEALSO jv-scan
922 gcc(1), gcj(1), gcjh(1), gij(1), jcf-dump(1), gfdl(7),
923 and the Info entries for @file{gcj} and @file{gcc}.
927 @c man begin OPTIONS jv-scan
931 Don't recognize the @code{assert} keyword, for backwards compatibility
932 with older versions of the language specification.
935 This prints a complexity measure, related to cyclomatic complexity, for
938 @item --encoding=@var{name}
939 This works like the corresponding @command{gcj} option.
942 This prints the name of the class in this file containing a @code{main}
946 This lists the names of all classes defined in the input files.
948 @item --list-filename
949 If @code{--list-class} is given, this option causes @code{jv-scan} to
950 also print the name of the file in which each class was found.
953 Print output to the named file.
956 Print help, then exit.
959 Print version number, then exit.
964 @node Invoking jcf-dump
965 @chapter Invoking jcf-dump
967 @c man title jcf-dump print information about Java class files
970 @c man begin SYNOPSIS jcf-dump
971 jcf-dump [@option{-c}] [@option{--javap}]
972 [@option{--classpath}=@var{path}] [@option{--CLASSPATH}=@var{path}]
973 [@option{-I}@var{dir}@dots{}] [@option{-o} @var{file}]
974 [@option{--version}] [@option{--help}] [@option{-v}] [@option{--verbose}]
975 @var{classname}@dots{}
977 @c man begin SEEALSO jcf-dump
978 gcc(1), gcj(1), gcjh(1), gij(1), jcf-dump(1), gfdl(7),
979 and the Info entries for @file{gcj} and @file{gcc}.
983 @c man begin DESCRIPTION jcf-dump
985 This is a class file examiner, similar to @code{javap}. It will print
986 information about a number of classes, which are specified by class name
991 @c man begin OPTIONS jcf-dump
995 Disassemble method bodies. By default method bodies are not printed.
997 @item --print-constants
998 Print the constant pool. When printing a reference to a constant
999 also print its index in the constant pool.
1002 Generate output in @code{javap} format. The implementation of this
1003 feature is very incomplete.
1005 @item --classpath=@var{path}
1006 @itemx --CLASSPATH=@var{path}
1007 @itemx -I@var{directory}
1008 @itemx -o @var{file}
1009 These options as the same as the corresponding @command{gcj} options.
1012 Print help, then exit.
1015 Print version number, then exit.
1018 Print extra information while running.
1019 Implies @code{--print-constants}.
1025 @chapter Invoking gij
1027 @c man title gij GNU interpreter for Java bytecode
1030 @c man begin SYNOPSIS gij
1031 gij [@option{OPTION}] @dots{} @var{JARFILE} [@var{ARGS}@dots{}]
1033 gij [@option{-jar}] [@option{OPTION}] @dots{} @var{CLASS} [@var{ARGS}@dots{}]
1034 [@option{-cp} @var{path}] [@option{-classpath} @var{path}]
1035 [@option{-D}@var{name}[=@var{value}]@dots{}]
1036 [@option{-ms=}@var{number}] [@option{-mx=}@var{number}]
1037 [@option{-X@var{argument}}] [@option{-verbose}] [@option{-verbose:class}]
1038 [@option{--showversion}] [@option{--version}] [@option{--help}][@option{-?}]
1040 @c man begin SEEALSO gij
1041 gcc(1), gcj(1), gcjh(1), jv-scan(1), jcf-dump(1), gfdl(7),
1042 and the Info entries for @file{gcj} and @file{gcc}.
1046 @c man begin DESCRIPTION gij
1048 @code{gij} is a Java bytecode interpreter included with @code{libgcj}.
1049 @code{gij} is not available on every platform; porting it requires a
1050 small amount of assembly programming which has not been done for all the
1051 targets supported by @command{gcj}.
1053 The primary argument to @code{gij} is the name of a class or, with
1054 @code{-jar}, a jar file. Options before this argument are interpreted
1055 by @code{gij}; remaining options are passed to the interpreted program.
1057 If a class name is specified and this class does not have a @code{main}
1058 method with the appropriate signature (a @code{static void} method with
1059 a @code{String[]} as its sole argument), then @code{gij} will print an
1062 If a jar file is specified then @code{gij} will use information in it to
1063 determine which class' @code{main} method will be invoked.
1065 @code{gij} will invoke the @code{main} method with all the remaining
1066 command-line options.
1068 Note that @code{gij} is not limited to interpreting code. Because
1069 @code{libgcj} includes a class loader which can dynamically load shared
1070 objects, it is possible to give @code{gij} the name of a class which has
1071 been compiled and put into a shared library on the class path.
1075 @c man begin OPTIONS gij
1078 @item -cp @var{path}
1079 @itemx -classpath @var{path}
1080 Set the initial class path. The class path is used for finding
1081 class and resource files. If specified, this option overrides the
1082 @code{CLASSPATH} environment variable. Note that this option is
1083 ignored if @code{-jar} is used.
1085 @item -D@var{name}[=@var{value}]
1086 This defines a system property named @var{name} with value @var{value}.
1087 If @var{value} is not specified then it defaults to the empty string.
1088 These system properties are initialized at the program's startup and can
1089 be retrieved at runtime using the @code{java.lang.System.getProperty}
1092 @item -ms=@var{number}
1093 Equivalent to @code{-Xms}.
1095 @item -mx=@var{number}
1096 Equivalent to @code{-Xmx}.
1099 Do not verify compliance of bytecode with the VM specification. In addition,
1100 this option disables type verification which is otherwise performed on BC-ABI
1104 @itemx -X@var{argument}
1105 Supplying @code{-X} by itself will cause @code{gij} to list all the
1106 supported @code{-X} options. Currently these options are supported:
1109 @item -Xms@var{size}
1110 Set the initial heap size.
1112 @item -Xmx@var{size}
1113 Set the maximum heap size.
1115 @item -Xss@var{size}
1116 Set the thread stack size.
1119 Unrecognized @code{-X} options are ignored, for compatibility with
1123 This indicates that the name passed to @code{gij} should be interpreted
1124 as the name of a jar file, not a class.
1128 Print help, then exit.
1131 Print version number and continue.
1134 Print detailed version information, then exit.
1137 Print version number, then exit.
1140 @itemx -verbose:class
1141 Each time a class is initialized, print a short message on standard error.
1144 @code{gij} also recognizes and ignores the following options, for
1145 compatibility with existing application launch scripts:
1146 @code{-client}, @code{-server}, @code{-hotspot}, @code{-jrockit},
1147 @code{-agentlib}, @code{-agentpath}, @code{-debug}, @code{-d32},
1148 @code{-d64}, @code{-javaagent}, @code{-noclassgc}, @code{-verify},
1149 and @code{-verifyremote}.
1153 @node Invoking gcj-dbtool
1154 @chapter Invoking gcj-dbtool.
1156 @c man title gcj-dbtool Manipulate class file mapping databases for libgcj
1159 @c man begin SYNOPSIS gcj-dbtool
1160 gcj-dbtool @option{OPTION} @var{DBFILE} [@option{MORE}] @dots{}
1162 gcj-dbtool [@option{-0}] [@option{-}] [@option{-n}] [@option{-a}] [@option{-f}]
1163 [@option{-t}] [@option{-l}] [@option{-p} [@var{LIBDIR}]]
1164 [@option{-v}] [@option{-m}] [@option{--version}] [@option{--help}]
1167 @c man begin SEEALSO gij
1168 gcc(1), gcj(1), gcjh(1), jv-scan(1), jcf-dump(1), gfdl(7),
1169 and the Info entries for @file{gcj} and @file{gcc}.
1173 @c man begin DESCRIPTION gcj-dbtool
1175 @code{gcj-dbtool} is a tool for creating and manipulating class file
1176 mapping databases. @code{libgcj} can use these databases to find a
1177 shared library corresponding to the bytecode representation of a
1178 class. This functionality is useful for ahead-of-time compilation of
1179 a program that has no knowledge of @code{gcj}.
1181 @code{gcj-dbtool} works best if all the jar files added to it are
1182 compiled using @code{-findirect-dispatch}.
1184 Note that @code{gcj-dbtool} is currently available as ``preview
1185 technology''. We believe it is a reasonable way to allow
1186 application-transparent ahead-of-time compilation, but this is an
1187 unexplored area. We welcome your comments.
1191 @c man begin OPTIONS gcj-dbtool
1194 @item -n @var{DBFILE} [@var{SIZE}]
1195 This creates a new database. Currently, databases cannot be resized;
1196 you can choose a larger initial size if desired. The default size is
1199 @item -a @var{DBFILE} @var{JARFILE} @var{LIB}
1200 @itemx -f @var{DBFILE} @var{JARFILE} @var{LIB}
1201 This adds a jar file to the database. For each class file in the jar,
1202 a cryptographic signature of the bytecode representation of the class
1203 is recorded in the database. At runtime, a class is looked up by its
1204 signature and the compiled form of the class is looked for in the
1205 corresponding shared library. The @option{-a} option will verify
1206 that @var{LIB} exists before adding it to the database; @option{-f}
1209 @item [@option{-}][@option{-0}] -m @var{DBFILE} @var{DBFILE},[@var{DBFILE}]
1210 Merge a number of databases. The output database overwrites any
1211 existing database. To add databases into an existing database,
1212 include the destination in the list of sources.
1214 If @option{-} or @option{-0} are used, the list of files to read is
1215 taken from standard input instead of the command line. For
1216 @option{-0}, Input filenames are terminated by a null character
1217 instead of by whitespace. Useful when arguments might contain white
1218 space. The GNU find -print0 option produces input suitable for this
1221 @item -t @var{DBFILE}
1224 @item -l @var{DBFILE}
1225 List the contents of a database.
1228 Print the name of the default database. If there is no default
1229 database, this prints a blank line. If @var{LIBDIR} is specified, use
1230 it instead of the default library directory component of the database
1234 Print a help message, then exit.
1238 Print version information, then exit.
1244 @node Invoking jv-convert
1245 @chapter Invoking jv-convert
1247 @c man title jv-convert Convert file from one encoding to another
1249 @c man begin SYNOPSIS jv-convert
1250 @command{jv-convert} [@option{OPTION}] @dots{} [@var{INPUTFILE} [@var{OUTPUTFILE}]]
1253 [@option{--encoding} @var{name}]
1254 [@option{--from} @var{name}]
1255 [@option{--to} @var{name}]
1256 [@option{-i} @var{file}] [@option{-o} @var{file}]
1257 [@option{--reverse}] [@option{--help}] [@option{--version}]
1261 @c man begin DESCRIPTION jv-convert
1263 @command{jv-convert} is a utility included with @code{libgcj} which
1264 converts a file from one encoding to another. It is similar to the Unix
1265 @command{iconv} utility.
1267 The encodings supported by @command{jv-convert} are platform-dependent.
1268 Currently there is no way to get a list of all supported encodings.
1272 @c man begin OPTIONS jv-convert
1275 @item --encoding @var{name}
1276 @itemx --from @var{name}
1277 Use @var{name} as the input encoding. The default is the current
1280 @item --to @var{name}
1281 Use @var{name} as the output encoding. The default is the
1282 @code{JavaSrc} encoding; this is ASCII with @samp{\u} escapes for
1283 non-ASCII characters.
1286 Read from @var{file}. The default is to read from standard input.
1289 Write to @var{file}. The default is to write to standard output.
1292 Swap the input and output encodings.
1295 Print a help message, then exit.
1298 Print version information, then exit.
1303 @node Invoking grmic
1304 @chapter Invoking grmic
1306 @c man title grmic Generate stubs for Remote Method Invocation
1308 @c man begin SYNOPSIS grmic
1309 @command{grmic} [@option{OPTION}] @dots{} @var{class} @dots{}
1312 [@option{-keepgenerated}]
1316 [@option{-nocompile}]
1318 [@option{-d} @var{directory}]
1324 @c man begin DESCRIPTION grmic
1326 @command{grmic} is a utility included with @code{libgcj} which generates
1327 stubs for remote objects.
1329 @c FIXME: Add real information here.
1330 @c This really isn't much more than the --help output.
1332 Note that this program isn't yet fully compatible with the JDK
1333 @command{grmic}. Some options, such as @option{-classpath}, are
1334 recognized but currently ignored. We have left these options
1335 undocumented for now.
1337 Long options can also be given with a GNU-style leading @samp{--}. For
1338 instance, @option{--help} is accepted.
1342 @c man begin OPTIONS grmic
1346 @itemx -keepgenerated
1347 By default, @command{grmic} deletes intermediate files. Either of these
1348 options causes it not to delete such files.
1351 Cause @command{grmic} to create stubs and skeletons for the 1.1
1355 Cause @command{grmic} to create stubs and skeletons compatible with both
1356 the 1.1 and 1.2 protocol versions. This is the default.
1359 Cause @command{grmic} to create stubs and skeletons for the 1.2
1363 Don't compile the generated files.
1366 Print information about what @command{grmic} is doing.
1368 @item -d @var{directory}
1369 Put output files in @var{directory}. By default the files are put in
1370 the current working directory.
1373 Print a help message, then exit.
1376 Print version information, then exit.
1382 @node Invoking grmiregistry
1383 @chapter Invoking grmiregistry
1385 @c man title grmiregistry Remote object registry
1387 @c man begin SYNOPSIS grmiregistry
1388 @command{grmic} [@option{OPTION}] @dots{} [@var{port}]
1391 [@option{--version}]
1395 @c man begin DESCRIPTION grmiregistry
1397 @command{grmiregistry} starts a remote object registry on the current
1398 host. If no port number is specified, then port 1099 is used.
1400 @c FIXME: Add real information here.
1401 @c This really isn't much more than the --help output.
1405 @c man begin OPTIONS grmiregistry
1409 Print a help message, then exit.
1412 Print version information, then exit.
1421 This documents CNI, the Compiled Native Interface,
1422 which is is a convenient way to write Java native methods using C++.
1423 This is a more efficient, more convenient, but less portable
1424 alternative to the standard JNI (Java Native Interface).
1427 * Basic concepts:: Introduction to using CNI@.
1428 * Packages:: How packages are mapped to C++.
1429 * Primitive types:: Handling Java types in C++.
1430 * Interfaces:: How Java interfaces map to C++.
1431 * Objects and Classes:: C++ and Java classes.
1432 * Class Initialization:: How objects are initialized.
1433 * Object allocation:: How to create Java objects in C++.
1434 * Memory allocation:: How to allocate and free memory.
1435 * Arrays:: Dealing with Java arrays in C++.
1436 * Methods:: Java methods in C++.
1437 * Strings:: Information about Java Strings.
1438 * Mixing with C++:: How CNI can interoperate with C++.
1439 * Exception Handling:: How exceptions are handled.
1440 * Synchronization:: Synchronizing between Java and C++.
1441 * Invocation:: Starting the Java runtime from C++.
1442 * Reflection:: Using reflection from C++.
1446 @node Basic concepts
1447 @section Basic concepts
1449 In terms of languages features, Java is mostly a subset
1450 of C++. Java has a few important extensions, plus a powerful standard
1451 class library, but on the whole that does not change the basic similarity.
1452 Java is a hybrid object-oriented language, with a few native types,
1453 in addition to class types. It is class-based, where a class may have
1454 static as well as per-object fields, and static as well as instance methods.
1455 Non-static methods may be virtual, and may be overloaded. Overloading is
1456 resolved at compile time by matching the actual argument types against
1457 the parameter types. Virtual methods are implemented using indirect calls
1458 through a dispatch table (virtual function table). Objects are
1459 allocated on the heap, and initialized using a constructor method.
1460 Classes are organized in a package hierarchy.
1462 All of the listed attributes are also true of C++, though C++ has
1463 extra features (for example in C++ objects may be allocated not just
1464 on the heap, but also statically or in a local stack frame). Because
1465 @command{gcj} uses the same compiler technology as G++ (the GNU
1466 C++ compiler), it is possible to make the intersection of the two
1467 languages use the same ABI (object representation and calling
1468 conventions). The key idea in CNI is that Java objects are C++
1469 objects, and all Java classes are C++ classes (but not the other way
1470 around). So the most important task in integrating Java and C++ is to
1471 remove gratuitous incompatibilities.
1473 You write CNI code as a regular C++ source file. (You do have to use
1474 a Java/CNI-aware C++ compiler, specifically a recent version of G++.)
1476 @noindent A CNI C++ source file must have:
1479 #include <gcj/cni.h>
1482 @noindent and then must include one header file for each Java class it uses, e.g.:
1485 #include <java/lang/Character.h>
1486 #include <java/util/Date.h>
1487 #include <java/lang/IndexOutOfBoundsException.h>
1490 @noindent These header files are automatically generated by @code{gcjh}.
1493 CNI provides some functions and macros to make using Java objects and
1494 primitive types from C++ easier. In general, these CNI functions and
1495 macros start with the @code{Jv} prefix, for example the function
1496 @code{JvNewObjectArray}. This convention is used to avoid conflicts
1497 with other libraries. Internal functions in CNI start with the prefix
1498 @code{_Jv_}. You should not call these; if you find a need to, let us
1499 know and we will try to come up with an alternate solution.
1502 @subsection Limitations
1504 Whilst a Java class is just a C++ class that doesn't mean that you are
1505 freed from the shackles of Java, a @acronym{CNI} C++ class must adhere to the
1506 rules of the Java programming language.
1508 For example: it is not possible to declare a method in a CNI class
1509 that will take a C string (@code{char*}) as an argument, or to declare a
1510 member variable of some non-Java datatype.
1516 The only global names in Java are class names, and packages. A
1517 @dfn{package} can contain zero or more classes, and also zero or more
1518 sub-packages. Every class belongs to either an unnamed package or a
1519 package that has a hierarchical and globally unique name.
1521 A Java package is mapped to a C++ @dfn{namespace}. The Java class
1522 @code{java.lang.String} is in the package @code{java.lang}, which is a
1523 sub-package of @code{java}. The C++ equivalent is the class
1524 @code{java::lang::String}, which is in the namespace @code{java::lang}
1525 which is in the namespace @code{java}.
1527 @noindent Here is how you could express this:
1530 (// @r{Declare the class(es), possibly in a header file:}
1539 class java::lang::String : public java::lang::Object
1545 @noindent The @code{gcjh} tool automatically generates the necessary namespace
1549 @subsection Leaving out package names
1551 Always using the fully-qualified name of a java class can be
1552 tiresomely verbose. Using the full qualified name also ties the code
1553 to a single package making code changes necessary should the class
1554 move from one package to another. The Java @code{package} declaration
1555 specifies that the following class declarations are in the named
1556 package, without having to explicitly name the full package
1557 qualifiers. The @code{package} declaration can be
1558 followed by zero or more @code{import} declarations, which
1559 allows either a single class or all the classes in a package to be
1560 named by a simple identifier. C++ provides something similar with the
1561 @code{using} declaration and directive.
1566 import @var{package-name}.@var{class-name};
1569 @noindent allows the program text to refer to @var{class-name} as a shorthand for
1570 the fully qualified name: @code{@var{package-name}.@var{class-name}}.
1573 @noindent To achieve the same effect C++, you have to do this:
1576 using @var{package-name}::@var{class-name};
1580 @noindent Java can also cause imports on demand, like this:
1583 import @var{package-name}.*;
1586 @noindent Doing this allows any class from the package @var{package-name} to be
1587 referred to only by its class-name within the program text.
1590 @noindent The same effect can be achieved in C++ like this:
1593 using namespace @var{package-name};
1597 @node Primitive types
1598 @section Primitive types
1600 Java provides 8 @dfn{primitives} types which represent integers, floats,
1601 characters and booleans (and also the void type). C++ has its own
1602 very similar concrete types. Such types in C++ however are not always
1603 implemented in the same way (an int might be 16, 32 or 64 bits for example)
1604 so CNI provides a special C++ type for each primitive Java type:
1606 @multitable @columnfractions .20 .25 .60
1607 @item @strong{Java type} @tab @strong{C/C++ typename} @tab @strong{Description}
1608 @item @code{char} @tab @code{jchar} @tab 16 bit Unicode character
1609 @item @code{boolean} @tab @code{jboolean} @tab logical (true or false) values
1610 @item @code{byte} @tab @code{jbyte} @tab 8-bit signed integer
1611 @item @code{short} @tab @code{jshort} @tab 16 bit signed integer
1612 @item @code{int} @tab @code{jint} @tab 32 bit signed integer
1613 @item @code{long} @tab @code{jlong} @tab 64 bit signed integer
1614 @item @code{float} @tab @code{jfloat} @tab 32 bit IEEE floating point number
1615 @item @code{double} @tab @code{jdouble} @tab 64 bit IEEE floating point number
1616 @item @code{void} @tab @code{void} @tab no value
1619 When referring to a Java type You should always use these C++ typenames (e.g.: @code{jint})
1620 to avoid disappointment.
1623 @subsection Reference types associated with primitive types
1625 In Java each primitive type has an associated reference type,
1626 e.g.: @code{boolean} has an associated @code{java.lang.Boolean} class.
1627 In order to make working with such classes easier GCJ provides the macro
1630 @deffn macro JvPrimClass type
1631 Return a pointer to the @code{Class} object corresponding to the type supplied.
1634 JvPrimClass(void) @result{} java.lang.Void.TYPE
1643 A Java class can @dfn{implement} zero or more
1644 @dfn{interfaces}, in addition to inheriting from
1645 a single base class.
1647 @acronym{CNI} allows CNI code to implement methods of interfaces.
1648 You can also call methods through interface references, with some
1651 @acronym{CNI} doesn't understand interface inheritance at all yet. So,
1652 you can only call an interface method when the declared type of the
1653 field being called matches the interface which declares that
1654 method. The workaround is to cast the interface reference to the right
1657 For example if you have:
1665 interface B extends A
1671 and declare a variable of type @code{B} in C++, you can't call
1672 @code{a()} unless you cast it to an @code{A} first.
1674 @node Objects and Classes
1675 @section Objects and Classes
1679 All Java classes are derived from @code{java.lang.Object}. C++ does
1680 not have a unique root class, but we use the C++ class
1681 @code{java::lang::Object} as the C++ version of the
1682 @code{java.lang.Object} Java class. All other Java classes are mapped
1683 into corresponding C++ classes derived from @code{java::lang::Object}.
1685 Interface inheritance (the @code{implements} keyword) is currently not
1686 reflected in the C++ mapping.
1689 @subsection Object fields
1691 Each object contains an object header, followed by the instance fields
1692 of the class, in order. The object header consists of a single
1693 pointer to a dispatch or virtual function table. (There may be extra
1694 fields @emph{in front of} the object, for example for memory
1695 management, but this is invisible to the application, and the
1696 reference to the object points to the dispatch table pointer.)
1698 The fields are laid out in the same order, alignment, and size as in
1699 C++. Specifically, 8-bit and 16-bit native types (@code{byte},
1700 @code{short}, @code{char}, and @code{boolean}) are @emph{not} widened
1701 to 32 bits. Note that the Java VM does extend 8-bit and 16-bit types
1702 to 32 bits when on the VM stack or temporary registers.
1704 If you include the @code{gcjh}-generated header for a
1705 class, you can access fields of Java classes in the @emph{natural}
1706 way. For example, given the following Java class:
1712 public Int (int i) @{ this.i = i; @}
1713 public static Int zero = new Int(0);
1720 #include <gcj/cni.h>;
1724 mult (Int *p, jint k)
1727 return Int::zero; // @r{Static member access.}
1728 return new Int(p->i * k);
1733 @subsection Access specifiers
1735 CNI does not strictly enforce the Java access
1736 specifiers, because Java permissions cannot be directly mapped
1737 into C++ permission. Private Java fields and methods are mapped
1738 to private C++ fields and methods, but other fields and methods
1739 are mapped to public fields and methods.
1743 @node Class Initialization
1744 @section Class Initialization
1746 Java requires that each class be automatically initialized at the time
1747 of the first active use. Initializing a class involves
1748 initializing the static fields, running code in class initializer
1749 methods, and initializing base classes. There may also be
1750 some implementation specific actions, such as allocating
1751 @code{String} objects corresponding to string literals in
1754 The GCJ compiler inserts calls to @code{JvInitClass} at appropriate
1755 places to ensure that a class is initialized when required. The C++
1756 compiler does not insert these calls automatically---it is the
1757 programmer's responsibility to make sure classes are initialized.
1758 However, this is fairly painless because of the conventions assumed by
1761 First, @code{libgcj} will make sure a class is initialized before an
1762 instance of that object is created. This is one of the
1763 responsibilities of the @code{new} operation. This is taken care of
1764 both in Java code, and in C++ code. When G++ sees a @code{new} of a
1765 Java class, it will call a routine in @code{libgcj} to allocate the
1766 object, and that routine will take care of initializing the class.
1767 Note however that this does not happen for Java arrays; you must
1768 allocate those using the appropriate CNI function. It follows that
1769 you can access an instance field, or call an instance (non-static)
1770 method and be safe in the knowledge that the class and all of its base
1771 classes have been initialized.
1773 Invoking a static method is also safe. This is because the
1774 Java compiler adds code to the start of a static method to make sure
1775 the class is initialized. However, the C++ compiler does not
1776 add this extra code. Hence, if you write a native static method
1777 using CNI, you are responsible for calling @code{JvInitClass}
1778 before doing anything else in the method (unless you are sure
1779 it is safe to leave it out).
1781 Accessing a static field also requires the class of the
1782 field to be initialized. The Java compiler will generate code
1783 to call @code{JvInitClass} before getting or setting the field.
1784 However, the C++ compiler will not generate this extra code,
1785 so it is your responsibility to make sure the class is
1786 initialized before you access a static field from C++.
1789 @node Object allocation
1790 @section Object allocation
1792 New Java objects are allocated using a
1793 @dfn{class instance creation expression}, e.g.:
1796 new @var{Type} ( ... )
1799 The same syntax is used in C++. The main difference is that
1800 C++ objects have to be explicitly deleted; in Java they are
1801 automatically deleted by the garbage collector.
1802 Using @acronym{CNI}, you can allocate a new Java object
1803 using standard C++ syntax and the C++ compiler will allocate
1804 memory from the garbage collector. If you have overloaded
1805 constructors, the compiler will choose the correct one
1806 using standard C++ overload resolution rules.
1808 @noindent For example:
1811 java::util::Hashtable *ht = new java::util::Hashtable(120);
1815 @node Memory allocation
1816 @section Memory allocation
1818 When allocating memory in @acronym{CNI} methods it is best to handle
1819 out-of-memory conditions by throwing a Java exception. These
1820 functions are provided for that purpose:
1822 @deftypefun void* JvMalloc (jsize @var{size})
1823 Calls malloc. Throws @code{java.lang.OutOfMemoryError} if allocation
1827 @deftypefun void* JvRealloc (void* @var{ptr}, jsize @var{size})
1828 Calls realloc. Throws @code{java.lang.OutOfMemoryError} if
1832 @deftypefun void JvFree (void* @var{ptr})
1839 While in many ways Java is similar to C and C++, it is quite different
1840 in its treatment of arrays. C arrays are based on the idea of pointer
1841 arithmetic, which would be incompatible with Java's security
1842 requirements. Java arrays are true objects (array types inherit from
1843 @code{java.lang.Object}). An array-valued variable is one that
1844 contains a reference (pointer) to an array object.
1846 Referencing a Java array in C++ code is done using the
1847 @code{JArray} template, which as defined as follows:
1850 class __JArray : public java::lang::Object
1857 class JArray : public __JArray
1861 T& operator[](jint i) @{ return data[i]; @}
1866 There are a number of @code{typedef}s which correspond to @code{typedef}s
1867 from the @acronym{JNI}. Each is the type of an array holding objects
1868 of the relevant type:
1871 typedef __JArray *jarray;
1872 typedef JArray<jobject> *jobjectArray;
1873 typedef JArray<jboolean> *jbooleanArray;
1874 typedef JArray<jbyte> *jbyteArray;
1875 typedef JArray<jchar> *jcharArray;
1876 typedef JArray<jshort> *jshortArray;
1877 typedef JArray<jint> *jintArray;
1878 typedef JArray<jlong> *jlongArray;
1879 typedef JArray<jfloat> *jfloatArray;
1880 typedef JArray<jdouble> *jdoubleArray;
1884 @deftypemethod {template<class T>} T* elements (JArray<T> @var{array})
1885 This template function can be used to get a pointer to the elements of
1886 the @code{array}. For instance, you can fetch a pointer to the
1887 integers that make up an @code{int[]} like so:
1890 extern jintArray foo;
1891 jint *intp = elements (foo);
1894 The name of this function may change in the future.
1898 @deftypefun jobjectArray JvNewObjectArray (jsize @var{length}, jclass @var{klass}, jobject @var{init})
1899 Here @code{klass} is the type of elements of the array and
1900 @code{init} is the initial value put into every slot in the array.
1904 @subsection Creating arrays
1906 For each primitive type there is a function which can be used to
1907 create a new array of that type. The name of the function is of the
1911 JvNew@var{Type}Array
1914 @noindent For example:
1920 @noindent can be used to create an array of Java primitive boolean types.
1922 @noindent The following function definition is the template for all such functions:
1924 @deftypefun jbooleanArray JvNewBooleanArray (jint @var{length})
1925 Create's an array @var{length} indices long.
1928 @deftypefun jsize JvGetArrayLength (jarray @var{array})
1929 Returns the length of the @var{array}.
1936 Java methods are mapped directly into C++ methods.
1937 The header files generated by @code{gcjh}
1938 include the appropriate method definitions.
1939 Basically, the generated methods have the same names and
1940 @emph{corresponding} types as the Java methods,
1941 and are called in the natural manner.
1943 @subsection Overloading
1945 Both Java and C++ provide method overloading, where multiple
1946 methods in a class have the same name, and the correct one is chosen
1947 (at compile time) depending on the argument types.
1948 The rules for choosing the correct method are (as expected) more complicated
1949 in C++ than in Java, but given a set of overloaded methods
1950 generated by @code{gcjh} the C++ compiler will choose
1953 Common assemblers and linkers are not aware of C++ overloading,
1954 so the standard implementation strategy is to encode the
1955 parameter types of a method into its assembly-level name.
1956 This encoding is called @dfn{mangling},
1957 and the encoded name is the @dfn{mangled name}.
1958 The same mechanism is used to implement Java overloading.
1959 For C++/Java interoperability, it is important that both the Java
1960 and C++ compilers use the @emph{same} encoding scheme.
1962 @subsection Static methods
1964 Static Java methods are invoked in @acronym{CNI} using the standard
1965 C++ syntax, using the @code{::} operator rather
1966 than the @code{.} operator.
1968 @noindent For example:
1971 jint i = java::lang::Math::round((jfloat) 2.3);
1974 @noindent C++ method definition syntax is used to define a static native method.
1978 #include <java/lang/Integer>
1979 java::lang::Integer*
1980 java::lang::Integer::getInteger(jstring str)
1987 @subsection Object Constructors
1989 Constructors are called implicitly as part of object allocation
1990 using the @code{new} operator.
1992 @noindent For example:
1995 java::lang::Integer *x = new java::lang::Integer(234);
1998 Java does not allow a constructor to be a native method.
1999 This limitation can be coded round however because a constructor
2000 can @emph{call} a native method.
2003 @subsection Instance methods
2005 Calling a Java instance method from a C++ @acronym{CNI} method is done
2006 using the standard C++ syntax, e.g.:
2009 // @r{First create the Java object.}
2010 java::lang::Integer *x = new java::lang::Integer(234);
2011 // @r{Now call a method.}
2012 jint prim_value = x->intValue();
2013 if (x->longValue == 0)
2017 @noindent Defining a Java native instance method is also done the natural way:
2020 #include <java/lang/Integer.h>
2023 java::lang:Integer::doubleValue()
2025 return (jdouble) value;
2030 @subsection Interface methods
2032 In Java you can call a method using an interface reference. This is
2033 supported, but not completely. @xref{Interfaces}.
2041 @acronym{CNI} provides a number of utility functions for
2042 working with Java Java @code{String} objects.
2043 The names and interfaces are analogous to those of @acronym{JNI}.
2046 @deftypefun jstring JvNewString (const char* @var{chars}, jsize @var{len})
2047 Returns a Java @code{String} object with characters from the C string
2048 @var{chars} up to the index @var{len} in that array.
2051 @deftypefun jstring JvNewStringLatin1 (const char* @var{bytes}, jsize @var{len})
2052 Returns a Java @code{String} made up of @var{len} bytes from @var{bytes}.
2056 @deftypefun jstring JvNewStringLatin1 (const char* @var{bytes})
2057 As above but the length of the @code{String} is @code{strlen(@var{bytes})}.
2060 @deftypefun jstring JvNewStringUTF (const char* @var{bytes})
2061 Returns a @code{String} which is made up of the UTF encoded characters
2062 present in the C string @var{bytes}.
2065 @deftypefun jchar* JvGetStringChars (jstring @var{str})
2066 Returns a pointer to an array of characters making up the @code{String} @var{str}.
2069 @deftypefun int JvGetStringUTFLength (jstring @var{str})
2070 Returns the number of bytes required to encode the contents of the
2071 @code{String} @var{str} in UTF-8.
2074 @deftypefun jsize JvGetStringUTFRegion (jstring @var{str}, jsize @var{start}, jsize @var{len}, char* @var{buf})
2075 Puts the UTF-8 encoding of a region of the @code{String} @var{str} into
2076 the buffer @code{buf}. The region to fetch is marked by @var{start} and @var{len}.
2078 Note that @var{buf} is a buffer, not a C string. It is @emph{not}
2083 @node Mixing with C++
2084 @section Interoperating with C/C++
2086 Because @acronym{CNI} is designed to represent Java classes and methods it
2087 cannot be mixed readily with C/C++ types.
2089 One important restriction is that Java classes cannot have non-Java
2090 type instance or static variables and cannot have methods which take
2091 non-Java types as arguments or return non-Java types.
2093 @noindent None of the following is possible with CNI:
2097 class ::MyClass : public java::lang::Object
2099 char* variable; // @r{char* is not a valid Java type.}
2104 ::SomeClass::someMethod (char *arg)
2109 @} // @r{@code{uint} is not a valid Java type, neither is @code{char*}}
2112 @noindent Of course, it is ok to use C/C++ types within the scope of a method:
2117 ::SomeClass::otherMethod (jstring str)
2128 The above restriction can be problematic, so @acronym{CNI} includes the
2129 @code{gnu.gcj.RawData} class. The @code{RawData} class is a
2130 @dfn{non-scanned reference} type. In other words variables declared
2131 of type @code{RawData} can contain any data and are not checked by the
2132 compiler or memory manager in any way.
2134 This means that you can put C/C++ data structures (including classes)
2135 in your @acronym{CNI} classes, as long as you use the appropriate cast.
2137 @noindent Here are some examples:
2141 class ::MyClass : public java::lang::Object
2143 gnu.gcj.RawData string;
2146 gnu.gcj.RawData getText ();
2150 ::MyClass::MyClass ()
2157 ::MyClass::getText ()
2163 ::MyClass::printText ()
2165 printf("%s\n", (char*) string);
2170 @subsection RawDataManaged
2172 @code{gnu.gcj.RawDataManaged} is another type used to indicate special data used
2173 by native code. Unlike the @code{RawData} type, fields declared as
2174 @code{RawDataManaged} will be "marked" by the memory manager and
2175 considered for garbage collection.
2177 Native data which is allocated using CNI's @code{JvAllocBytes()}
2178 function and stored in a @code{RawDataManaged} will be automatically
2179 freed when the Java object it is associated with becomes unreachable.
2181 @subsection Native memory allocation
2183 @deftypefun void* JvAllocBytes (jsize @var{size})
2184 Allocates @var{size} bytes from the heap. The memory returned is zeroed.
2185 This memory is not scanned for pointers by the garbage collector, but will
2186 be freed if no references to it are discovered.
2188 This function can be useful if you need to associate some native data with a
2189 Java object. Using a CNI's special @code{RawDataManaged} type, native data
2190 allocated with @code{JvAllocBytes} will be automatically freed when the Java
2191 object itself becomes unreachable.
2194 @subsection Posix signals
2196 On Posix based systems the @code{libgcj} library uses several signals
2197 internally. @acronym{CNI} code should not attempt to use the same
2198 signals as doing so may cause @code{libgcj} and/or the @acronym{CNI}
2201 SIGSEGV is used on many systems to generate
2202 @code{NullPointerExceptions}. SIGCHLD is used internally by
2203 @code{Runtime.exec()}. Several other signals (that vary from platform to
2204 platform) can be used by the memory manager and by
2205 @code{Thread.interrupt()}.
2207 @node Exception Handling
2208 @section Exception Handling
2210 While C++ and Java share a common exception handling framework,
2211 things are not yet perfectly integrated. The main issue is that the
2212 run-time type information facilities of the two
2213 languages are not integrated.
2215 Still, things work fairly well. You can throw a Java exception from
2216 C++ using the ordinary @code{throw} construct, and this
2217 exception can be caught by Java code. Similarly, you can catch an
2218 exception thrown from Java using the C++ @code{catch}
2221 @noindent Here is an example:
2225 throw new java::lang::IndexOutOfBoundsException();
2228 Normally, G++ will automatically detect when you are writing C++
2229 code that uses Java exceptions, and handle them appropriately.
2230 However, if C++ code only needs to execute destructors when Java
2231 exceptions are thrown through it, GCC will guess incorrectly. Sample
2235 struct S @{ ~S(); @};
2237 extern void bar(); // @r{Is implemented in Java and may throw exceptions.}
2246 The usual effect of an incorrect guess is a link failure, complaining of
2247 a missing routine called @code{__gxx_personality_v0}.
2249 You can inform the compiler that Java exceptions are to be used in a
2250 translation unit, irrespective of what it might think, by writing
2251 @code{#pragma GCC java_exceptions} at the head of the
2252 file. This @code{#pragma} must appear before any
2253 functions that throw or catch exceptions, or run destructors when
2254 exceptions are thrown through them.
2256 @node Synchronization
2257 @section Synchronization
2259 Each Java object has an implicit monitor.
2260 The Java VM uses the instruction @code{monitorenter} to acquire
2261 and lock a monitor, and @code{monitorexit} to release it.
2263 The corresponding CNI macros are @code{JvMonitorEnter} and
2264 @code{JvMonitorExit} (JNI has similar methods @code{MonitorEnter}
2265 and @code{MonitorExit}).
2268 The Java source language does not provide direct access to these primitives.
2269 Instead, there is a @code{synchronized} statement that does an
2270 implicit @code{monitorenter} before entry to the block,
2271 and does a @code{monitorexit} on exit from the block.
2272 Note that the lock has to be released even when the block is abnormally
2273 terminated by an exception, which means there is an implicit
2274 @code{try finally} surrounding synchronization locks.
2276 From C++, it makes sense to use a destructor to release a lock.
2277 @acronym{CNI} defines the following utility class:
2280 class JvSynchronize() @{
2282 JvSynchronize(jobject o) @{ obj = o; JvMonitorEnter(o); @}
2283 ~JvSynchronize() @{ JvMonitorExit(obj); @}
2296 @noindent might become this C++ code:
2300 JvSynchronize dummy (OBJ);
2305 Java also has methods with the @code{synchronized} attribute.
2306 This is equivalent to wrapping the entire method body in a
2307 @code{synchronized} statement.
2308 (Alternatively, an implementation could require the caller to do
2309 the synchronization. This is not practical for a compiler, because
2310 each virtual method call would have to test at run-time if
2311 synchronization is needed.) Since in @command{gcj}
2312 the @code{synchronized} attribute is handled by the
2313 method implementation, it is up to the programmer
2314 of a synchronized native method to handle the synchronization
2315 (in the C++ implementation of the method).
2316 In other words, you need to manually add @code{JvSynchronize}
2317 in a @code{native synchronized} method.
2322 CNI permits C++ applications to make calls into Java classes, in addition to
2323 allowing Java code to call into C++. Several functions, known as the
2324 @dfn{invocation API}, are provided to support this.
2326 @deftypefun jint JvCreateJavaVM (JvVMInitArgs* @var{vm_args})
2328 Initializes the Java runtime. This function performs essential initialization
2329 of the threads interface, garbage collector, exception handling and other key
2330 aspects of the runtime. It must be called once by an application with
2331 a non-Java @code{main()} function, before any other Java or CNI calls are made.
2332 It is safe, but not recommended, to call @code{JvCreateJavaVM()} more than
2333 once provided it is only called from a single thread.
2334 The @var{vmargs} parameter can be used to specify initialization parameters
2335 for the Java runtime. It may be @code{NULL}.
2337 JvVMInitArgs represents a list of virtual machine initialization
2338 arguments. @code{JvCreateJavaVM()} ignores the version field.
2341 typedef struct JvVMOption
2343 // a VM initialization option
2345 // extra information associated with this option
2349 typedef struct JvVMInitArgs
2351 // for compatibility with JavaVMInitArgs
2354 // number of VM initialization options
2357 // an array of VM initialization options
2358 JvVMOption* options;
2360 // true if the option parser should ignore unrecognized options
2361 jboolean ignoreUnrecognized;
2365 @code{JvCreateJavaVM()} returns @code{0} upon success, or @code{-1} if
2366 the runtime is already initialized.
2368 @emph{Note:} In GCJ 3.1, the @code{vm_args} parameter is ignored. It
2369 is recognized and used as of release 4.0.
2372 @deftypefun java::lang::Thread* JvAttachCurrentThread (jstring @var{name}, java::lang::ThreadGroup* @var{group})
2373 Registers an existing thread with the Java runtime. This must be called once
2374 from each thread, before that thread makes any other Java or CNI calls. It
2375 must be called after @code{JvCreateJavaVM}.
2376 @var{name} specifies a name for the thread. It may be @code{NULL}, in which
2377 case a name will be generated.
2378 @var{group} is the ThreadGroup in which this thread will be a member. If it
2379 is @code{NULL}, the thread will be a member of the main thread group.
2380 The return value is the Java @code{Thread} object that represents the thread.
2381 It is safe to call @code{JvAttachCurrentThread()} more than once from the same
2382 thread. If the thread is already attached, the call is ignored and the current
2383 thread object is returned.
2386 @deftypefun jint JvDetachCurrentThread ()
2387 Unregisters a thread from the Java runtime. This should be called by threads
2388 that were attached using @code{JvAttachCurrentThread()}, after they have
2389 finished making calls to Java code. This ensures that any resources associated
2390 with the thread become eligible for garbage collection.
2391 This function returns @code{0} upon success, or @code{-1} if the current thread
2395 @subsection Handling uncaught exceptions
2397 If an exception is thrown from Java code called using the invocation API, and
2398 no handler for the exception can be found, the runtime will abort the
2399 application. In order to make the application more robust, it is recommended
2400 that code which uses the invocation API be wrapped by a top-level try/catch
2401 block that catches all Java exceptions.
2405 The following code demonstrates the use of the invocation API. In this
2406 example, the C++ application initializes the Java runtime and attaches
2407 itself. The @code{java.lang.System} class is initialized in order to
2408 access its @code{out} field, and a Java string is printed. Finally, the thread
2409 is detached from the runtime once it has finished making Java calls. Everything
2410 is wrapped with a try/catch block to provide a default handler for any uncaught
2413 The example can be compiled with @command{c++ test.cc -lgcj}.
2417 #include <gcj/cni.h>
2418 #include <java/lang/System.h>
2419 #include <java/io/PrintStream.h>
2420 #include <java/lang/Throwable.h>
2422 int main(int argc, char *argv)
2424 using namespace java::lang;
2428 JvCreateJavaVM(NULL);
2429 JvAttachCurrentThread(NULL, NULL);
2431 String *message = JvNewStringLatin1("Hello from C++");
2432 JvInitClass(&System::class$);
2433 System::out->println(message);
2435 JvDetachCurrentThread();
2437 catch (Throwable *t)
2439 System::err->println(JvNewStringLatin1("Unhandled Java exception:"));
2440 t->printStackTrace();
2448 Reflection is possible with CNI code, it functions similarly to how it
2449 functions with JNI@.
2451 @c clean this up... I mean, what are the types jfieldID and jmethodID in JNI?
2452 The types @code{jfieldID} and @code{jmethodID}
2455 @noindent The functions:
2458 @item @code{JvFromReflectedField},
2459 @item @code{JvFromReflectedMethod},
2460 @item @code{JvToReflectedField}
2461 @item @code{JvToFromReflectedMethod}
2464 @noindent will be added shortly, as will other functions corresponding to JNI@.
2467 @node System properties
2468 @chapter System properties
2470 The runtime behavior of the @code{libgcj} library can be modified by setting
2471 certain system properties. These properties can be compiled into the program
2472 using the @code{-D@var{name}[=@var{value}]} option to @command{gcj} or by
2473 setting them explicitly in the program by calling the
2474 @code{java.lang.System.setProperty()} method. Some system properties are only
2475 used for informational purposes (like giving a version number or a user name).
2476 A program can inspect the current value of a property by calling the
2477 @code{java.lang.System.getProperty()} method.
2480 * Standard Properties:: Standard properties supported by @code{libgcj}
2481 * GNU Classpath Properties:: Properties found in Classpath based libraries
2482 * libgcj Runtime Properties:: Properties specific to @code{libgcj}
2485 @node Standard Properties
2486 @section Standard Properties
2488 The following properties are normally found in all implementations of the core
2489 libraries for the Java language.
2494 The @code{libgcj} version number.
2497 Set to @samp{The Free Software Foundation, Inc.}
2499 @item java.vendor.url
2500 Set to @uref{http://gcc.gnu.org/java/}.
2503 The directory where @code{gcj} was installed. Taken from the @code{--prefix}
2504 option given to @command{configure}.
2506 @item java.class.version
2507 The class format version number supported by the libgcj byte code interpreter.
2508 (Currently @samp{46.0})
2510 @item java.vm.specification.version
2511 The Virtual Machine Specification version implemented by @code{libgcj}.
2512 (Currently @samp{1.0})
2514 @item java.vm.specification.vendor
2515 The name of the Virtual Machine specification designer.
2517 @item java.vm.specification.name
2518 The name of the Virtual Machine specification
2519 (Set to @samp{Java Virtual Machine Specification}).
2521 @item java.vm.version
2522 The @command{gcj} version number.
2524 @item java.vm.vendor
2525 Set to @samp{The Free Software Foundation, Inc.}
2528 Set to @samp{GNU libgcj}.
2530 @item java.specification.version
2531 The Runtime Environment specification version implemented by @code{libgcj}.
2532 (Currently set to @samp{1.3})
2534 @item java.specification.vendor
2535 The Runtime Environment specification designer.
2537 @item java.specification.name
2538 The name of the Runtime Environment specification
2539 (Set to @samp{Java Platform API Specification}).
2541 @item java.class.path
2542 The paths (jar files, zip files and directories) used for finding class files.
2544 @item java.library.path
2545 Directory path used for finding native libraries.
2547 @item java.io.tmpdir
2548 The directory used to put temporary files in.
2551 Name of the Just In Time compiler to use by the byte code interpreter.
2552 Currently not used in @code{libgcj}.
2555 Directories containing jar files with extra libraries. Will be used when
2558 @item java.protocol.handler.pkgs
2559 A @samp{|} separated list of package names that is used to find classes that
2560 implement handlers for @code{java.net.URL}.
2562 @item java.rmi.server.codebase
2563 A list of URLs that is used by the @code{java.rmi.server.RMIClassLoader}
2564 to load classes from.
2567 A list of class names that will be loaded by the @code{java.sql.DriverManager}
2570 @item file.separator
2571 The separator used in when directories are included in a filename
2572 (normally @samp{/} or @samp{\} ).
2575 The default character encoding used when converting platform native files to
2576 Unicode (usually set to @samp{8859_1}).
2578 @item path.separator
2579 The standard separator used when a string contains multiple paths
2580 (normally @samp{:} or @samp{;}), the string is usually not a valid character
2581 to use in normal directory names.)
2583 @item line.separator
2584 The default line separator used on the platform (normally @samp{\n}, @samp{\r}
2585 or a combination of those two characters).
2587 @item policy.provider
2588 The class name used for the default policy provider returned by
2589 @code{java.security.Policy.getPolicy}.
2592 The name of the user running the program. Can be the full name, the login name
2593 or empty if unknown.
2596 The default directory to put user specific files in.
2599 The current working directory from which the program was started.
2602 The default language as used by the @code{java.util.Locale} class.
2605 The default region as used by the @code{java.util.Local} class.
2608 The default variant of the language and region local used.
2611 The default timezone as used by the @code{java.util.TimeZone} class.
2614 The operating system/kernel name that the program runs on.
2617 The hardware that we are running on.
2620 The version number of the operating system/kernel.
2622 @item awt.appletWarning
2623 The string to display when an untrusted applet is displayed.
2624 Returned by @code{java.awt.Window.getWarningString()} when the window is
2628 The class name used for initializing the default @code{java.awt.Toolkit}.
2629 Defaults to @code{gnu.awt.gtk.GtkToolkit}.
2631 @item http.proxyHost
2632 Name of proxy host for http connections.
2634 @item http.proxyPort
2635 Port number to use when a proxy host is in use.
2639 @node GNU Classpath Properties
2640 @section GNU Classpath Properties
2642 @code{libgcj} is based on the GNU Classpath (Essential Libraries for Java) a
2643 GNU project to create free core class libraries for use with virtual machines
2644 and compilers for the Java language. The following properties are common to
2645 libraries based on GNU Classpath.
2649 @item gcj.dumpobject
2650 Enables printing serialization debugging by the @code{java.io.ObjectInput} and
2651 @code{java.io.ObjectOutput} classes when set to something else then the empty
2652 string. Only used when running a debug build of the library.
2654 @item gnu.classpath.vm.shortname
2655 This is a succinct name of the virtual machine. For @code{libgcj},
2656 this will always be @samp{libgcj}.
2658 @item gnu.classpath.home.url
2659 A base URL used for finding system property files (e.g.,
2660 @file{classpath.security}). By default this is a @samp{file:} URL
2661 pointing to the @file{lib} directory under @samp{java.home}.
2665 @node libgcj Runtime Properties
2666 @section libgcj Runtime Properties
2668 The following properties are specific to the @code{libgcj} runtime and will
2669 normally not be found in other core libraries for the java language.
2673 @item java.fullversion
2674 The combination of @code{java.vm.name} and @code{java.vm.version}.
2677 Same as @code{java.fullversion}.
2680 Used by the @code{java.net.DatagramSocket} class when set to something else
2681 then the empty string. When set all newly created @code{DatagramSocket}s will
2682 try to load a class @code{java.net.[impl.prefix]DatagramSocketImpl} instead of
2683 the normal @code{java.net.PlainDatagramSocketImpl}.
2685 @item gnu.gcj.progname
2686 The class or binary name that was used to invoke the program. This will be
2687 the name of the "main" class in the case where the @code{gij} front end is
2688 used, or the program binary name in the case where an application is compiled
2691 @item gnu.gcj.runtime.NameFinder.use_addr2line
2692 Whether an external process, @command{addr2line}, should be used to determine
2693 line number information when tracing the stack. Setting this to @code{false}
2694 may suppress line numbers when printing stack traces and when using
2695 the java.util.logging infrastructure. However, performance may improve
2696 significantly for applications that print stack traces or make logging calls
2699 @item gnu.gcj.runtime.VMClassLoader.library_control
2700 This controls how shared libraries are automatically loaded by the
2701 built-in class loader. If this property is set to @samp{full}, a full
2702 search is done for each requested class. If this property is set to
2703 @samp{cache} (the default), then any failed lookups are cached and not
2704 tried again. If this property is set to @samp{never}, then lookups
2705 are never done. For more information, @xref{Extensions}.
2707 @item gnu.gcj.runtime.endorsed.dirs
2708 This is like the standard @code{java.endorsed.dirs}, property, but
2709 specifies some extra directories which are searched after the standard
2710 endorsed directories. This is primarily useful for telling
2711 @code{libgcj} about additional libraries which are ordinarily
2712 incorporated into the JDK, and which should be loaded by the bootstrap
2713 class loader, but which are not yet part of @code{libgcj} itself for
2716 @item gnu.gcj.jit.compiler
2717 @c FIXME we should probably have a whole node on this...
2718 This is the full path to @command{gcj} executable which should be
2719 used to compile classes just-in-time when
2720 @code{ClassLoader.defineClass} is called. If not set, @command{gcj}
2721 will not be invoked by the runtime; this can also be controlled via
2722 @code{Compiler.disable}.
2724 @item gnu.gcj.jit.options
2725 This is a space-separated string of options which should be passed to
2726 @command{gcj} when in JIT mode. If not set, a sensible default is
2729 @item gnu.gcj.jit.cachedir
2730 This is the directory where cached shared library files are
2731 stored. If not set, JIT compilation is disabled. This should never
2732 be set to a directory that is writable by any other user.
2734 @item gnu.gcj.precompiled.db.path
2735 This is a sequence of file names, each referring to a file created by
2736 @command{gcj-dbtool}. These files will be used by @code{libgcj} to
2737 find shared libraries corresponding to classes that are loaded from
2738 bytecode. @code{libgcj} often has a built-in default database; it
2739 can be queried using @code{gcj-dbtool -p}.
2747 While writing @command{gcj} and @code{libgcj} we have, of course, relied
2748 heavily on documentation from Sun Microsystems. In particular we have
2749 used The Java Language Specification (both first and second editions),
2750 the Java Class Libraries (volumes one and two), and the Java Virtual
2751 Machine Specification. In addition we've used the online documentation
2752 at @uref{http://java.sun.com/}.
2754 The current @command{gcj} home page is
2755 @uref{http://gcc.gnu.org/java/}.
2757 For more information on gcc, see @uref{http://gcc.gnu.org/}.
2759 Some @code{libgcj} testing is done using the Mauve test suite. This is
2760 a free software Java class library test suite which is being written
2761 because the JCK is not free. See
2762 @uref{http://sources.redhat.com/mauve/} for more information.