javac(1)                   OpenBSD Reference Manual                   javac(1)



NAME
       javac - Java programming language compiler

SYNOPSIS
       javac [ options ] [ sourcefiles ] [ @argfiles ]


       Arguments may be in any order.

             options
                Command-line options.

             sourcefiles
                One or more source files to be compiled (such as
                MyClass.java).

             @argfiles
                One or more files that lists options and source files. The -J
                options are not allowed in these files.


DESCRIPTION
       The javac tool reads class and interface definitions, written in the
       Java programming language, and compiles them into bytecode class files.

       There are two ways to pass source code filenames to javac:

          o For a small number of source files, simply list the file names on
            the command line.

          o For a large number of source files, list the file names in a file,
            separated by blanks or line breaks. Then use the list file name on
            the javac command line, preceded by an @ character.


       Source code file names must have .java suffixes, class file names must
       have .class suffixes, and both source and class files must have root
       names that identify the class. For example, a class called MyClass
       would be written in a source file called MyClass.java and compiled into
       a bytecode class file called MyClass.class.

       Inner class definitions produce additional class files. These class
       files have names combining the inner and outer class names, such as
       MyClass$MyInnerClass.class.

       You should arrange source files in a directory tree that reflects their
       package tree. For example, if you keep all your source files in
       /workspace, the source code for com.mysoft.mypack.MyClass should be in
       /workspace/com/mysoft/mypack/MyClass.java.

       By default, the compiler puts each class file in the same directory as
       its source file. You can specify a separate destination directory with
       -d (see Options, below).

SEARCHING FOR TYPES
       When compiling a source file, the compiler often needs information
       about a type whose definition did not appear in the source files given
       on the command line. The compiler needs type information for every
       class or interface used, extended, or implemented in the source file.
       This includes classes and interfaces not explicitly mentioned in the
       source file but which provide information through inheritance.

       For example, when you subclass java.applet.Applet, you are also using
       Applet's ancestor classes: java.awt.Panel, java.awt.Container,
       java.awt.Component, and java.lang.Object.

       When the compiler needs type information, it looks for a source file or
       class file which defines the type. The compiler searches for class
       files first in the bootstrap and extension classes, then in the user
       class path (which by default is the current directory). The user class
       path is defined by setting the CLASSPATH environment variable or by
       using the -classpath command line option. (For details, see Setting the
       Class Path).

       If you set the -sourcepath option, the compiler searches the indicated
       path for source files; otherwise the compiler searches the user class
       path for both class files and source files.

       You can specify different bootstrap or extension classes with the
       -bootclasspath and -extdirs options; see Cross-Compilation Options
       below.

       A successful type search may produce a class file, a source file, or
       both. Here is how javac handles each situation:

          o Search produces a class file but no source file: javac uses the
            class file.

          o Search produces a source file but no class file: javac compiles
            the source file and uses the resulting class file.

          o Search produces both a source file and a class file: javac
            determines whether the class file is out of date. If the class
            file is out of date, javac recompiles the source file and uses the
            updated class file. Otherwise, javac just uses the class file.

          javac considers a class file out of date only if it is older than
          the source file.


       Note:   javac can silently compile source files not mentioned on the
       command line. Use the -verbose option to trace automatic compilation.

OPTIONS
       The compiler has a set of standard options that are supported on the
       current development environment and will be supported in future
       releases. An additional set of non-standard options are specific to the
       current virtual machine and compiler implementations and are subject to
       change in the future. Non-standard options begin with -X.

   Standard Options
             -classpath classpath
                Set the user class path, overriding the user class path in the
                CLASSPATH environment variable. If neither CLASSPATH or
                -classpath is specified, the user class path consists of the
                current directory. See Setting the Class Path for more
                details.

             If the -sourcepath option is not specified, the user class path
             is searched for both source files and class files.

             As a special convenience, a class path element containing a
             basename of * is considered equivalent to specifying a list of
             all the files in the directory with the extension .jar or .JAR (a
             java program cannot tell the difference between the two
             invocations).
             For example, if directory foo contains a.jar and b.JAR, then the
             class path element foo/* is expanded to a A.jar:b.JAR, except
             that the order of jar files is unspecified. All jar files in the
             specified directory, even hidden ones, are included in the list.
             A classpath entry consisting simply of * expands to a list of all
             the jar files in the current directory. The CLASSPATH environment
             variable, where defined, will be similarly expanded. Any
             classpath wildcard expansion occurs before the Java virtual
             machine is started -- no Java program will ever see unexpanded
             wildcards except by querying the environment. For example; by
             invoking System.getenv("CLASSPATH").

             -Djava.ext.dirs=directories
                Override the location of installed extensions.

             -Djava.endorsed.dirs=directories
                Override the location of endorsed standards path.

             -d directory
                Set the destination directory for class files. The destination
                directory must already exist; javac will not create the
                destination directory. If a class is part of a package, javac
                puts the class file in a subdirectory reflecting the package
                name, creating directories as needed. For example, if you
                specify -d /home/myclasses and the class is called
                com.mypackage.MyClass, then the class file is called
                /home/myclasses/com/mypackage/MyClass.class.

             If -d is not specified, javac puts the class file in the same
             directory as the source file.

             Note:   The directory specified by -d is not automatically added
             to your user class path.

             -deprecation
                Show a description of each use or override of a deprecated
                member or class. Without -deprecation, javac shows the names
                of source files that use or override deprecated members or
                classes. -deprecation is shorthand for -Xlint:deprecation.

             -encoding encoding
                Set the source file encoding name, such as EUC-JP and UTF-8..
                If -encoding is not specified, the platform default converter
                is used.

             -g Generate all debugging information, including local variables.
                By default, only line number and source file information is
                generated.

             -g:none
                Do not generate any debugging information.

             -g:{keyword list}
                Generate only some kinds of debugging information, specified
                by a comma separated list of keywords. Valid keywords are:

                source
                   Source file debugging information

                lines
                   Line number debugging information

                vars
                   Local variable debugging information

             -help
                Print a synopsis of standard options.

             -nowarn
                Disable warning messages. This has the same meaning as
                -Xlint:none.

             -source release
                Specifies the version of source code accepted. The following
                values for release are allowed:

                1.3
                   The compiler does not support assertions, generics, or
                   other language features introduced after JDK 1.3.

                1.4
                   The compiler accepts code containing assertions, which were
                   introduced in JDK 1.4.

                1.5
                   The compiler accepts code containing generics and other
                   language features introduced in JDK 5. This is the default.

                5  Synonym for 1.5
             Note: No language changes were introduced in JDK 6, so the values
             1.6 and 6 are not valid.

             -sourcepath sourcepath
                Specify the source code path to search for class or interface
                definitions. As with the user class path, source path entries
                are separated by colons (:) and can be directories, JAR
                archives, or ZIP archives. If packages are used, the local
                path name within the directory or archive must reflect the
                package name.

             Note:   Classes found through the classpath are subject to
             automatic recompilation if their sources are found.

             -verbose
                Verbose output. This includes information about each class
                loaded and each source file compiled.

             -X Display information about non-standard options and exit.


   Cross-Compilation Options
          By default, classes are compiled against the bootstrap and extension
          classes of the platform that javac shipped with. But javac also
          supports cross-compiling, where classes are compiled against a
          bootstrap and extension classes of a different Java platform
          implementation. It is important to use -bootclasspath and -extdirs
          when cross-compiling; see Cross-Compilation Example below.

             -target version
                Generate class files that target a specified version of the
                VM. Class files will run on the specified target and on later
                versions, but not on earlier versions of the VM. Valid targets
                are 1.1 1.2 1.3 1.4 1.5 (also 5) and 1.6 (also 6).

             The default for -target depends on the value of -source:

                o If -source is not specified, the value of -target is 1.6

                o If -source is 1.3, the value of -target is 1.1

                o For all other values of -source, the value of -target is the
                  value of -source.

             -bootclasspath bootclasspath
                Cross-compile against the specified set of boot classes. As
                with the user class path, boot class path entries are
                separated by colons (:) and can be directories, JAR archives,
                or ZIP archives.

             -extdirs directories
                Cross-compile against the specified extension directories.
                Directories is a colon-separated list of directories. Each JAR
                archive in the specified directories is searched for class
                files.


   Non-Standard Options
             -Xbootclasspath/p:path
                Prepend to the bootstrap class path.

             -Xbootclasspath/a:path
                Append to the bootstrap class path.

             -Xbootclasspath/:path
                Override location of bootstrap class files.

             -Xlint
                Enable all recommended warnings. In this release, all
                available warnings are recommended.

             -Xlint:none
                Disable all warnings not mandated by the Java Language
                Specification.

             -Xlint:-xxx
                Disable warning xxx, where xxx is one of the warning names
                supported for -Xlint:xxx, below

             -Xlint:unchecked
                Give more detail for unchecked conversion warnings that are
                mandated by the Java Language Specification.

             -Xlint:path
                Warn about nonexistent path (classpath, sourcepath, etc)
                directories.

             -Xlint:serial
                Warn about missing serialVersionUID definitions on
                serializable classes.

             -Xlint:finally
                Warn about finally clauses that cannot complete normally.

             -Xlint:fallthrough
                Check switch blocks for fall-through cases and provide a
                warning message for any that are found. Fall-through cases are
                cases in a switch block, other than the last case in the
                block, whose code does not include a break statement, allowing
                code execution to "fall through" from that case to the next
                case. For example, the code following the case 1 label in this
                switch block does not contain a break statement:


                switch (x) {
                case 1:
                       System.out.println("1");
                       //  No  break;  statement here.
                case 2:
                       System.out.println("2");
                }
             If the -Xlint:fallthrough flag were used when compiling this
             code, the compiler would emit a warning about "possible
             fall-through into case," along with the line number of the case
             in question.

             -Xmaxerrors number
                Set the maximum number of errors to print.

             -Xmaxwarns number
                Set the maximum number of warnings to print.

             -Xstdout filename
                Send compiler messages to the named file. By default, compiler
                messages go to System.err.


   The -J Option
             -Joption
                Pass option to the java launcher called by javac. For example,
                -J-Xms48m sets the startup memory to 48 megabytes. Although it
                does not begin with -X, it is not a `standard option' of
                javac. It is a common convention for -J to pass options to the
                underlying VM executing applications written in Java.

             Note:   CLASSPATH, -classpath, -bootclasspath, and -extdirs do
             not specify the classes used to run javac. Fiddling with the
             implementation of the compiler in this way is usually pointless
             and always risky. If you do need to do this, use the -J option to
             pass through options to the underlying java launcher.


COMMAND LINE ARGUMENT FILES
       To shorten or simplify the javac command line, you can specify one or
       more files that themselves contain arguments to the javac command
       (except -J options). This enables you to create javac commands of any
       length on any operating system.

       An argument file can include javac options and source filenames in any
       combination. The arguments within a file can be space-separated or
       newline-separated. If a filename contains embedded spaces, put the
       whole filename in double quotes.

       Filenames within an argument file are relative to the current
       directory, not the location of the argument file. Wildcards (*) are not
       allowed in these lists (such as for specifying *.java). Use of the '@'
       character to recursively interpret files is not supported. The -J
       options are not supported because they are passed to the launcher,
       which does not support argument files.

       When executing javac, pass in the path and name of each argument file
       with the '@' leading character. When javac encounters an argument
       beginning with the character `@', it expands the contents of that file
       into the argument list.

   Example - Single Arg File
       You could use a single argument file named "argfile" to hold all javac
       arguments:

         C:> javac @argfile


       This argument file could contain the contents of both files shown in
       the next example.

   Example - Two Arg Files
       You can create two argument files -- one for the javac options and the
       other for the source filenames: (Notice the following lists have no
       line-continuation characters.)

       Create a file named "options" containing:

            -d classes
            -g
            -sourcepath \java\pubs\ws\1.3\src\share\classes


       Create a file named "classes" containing:

            MyClass1.java
            MyClass2.java
            MyClass3.java


       You would then run javac with:

         % javac @options @classes


   Example - Arg Files with Paths
       The argument files can have paths, but any filenames inside the files
       are relative to the current working directory (not path1 or path2):

         % javac @path1/options @path2/classes


PROGRAMMATIC INTERFACE
       The com.sun.tools.javac.Main class provides two static methods to
       invoke the compiler from a program:

       public static int compile(String[] args);
       public static int compile(String[] args, PrintWriter out);


       The args parameter represents any of the command line arguments that
       would normally be passed to the javac program and are outlined in the
       above Synopsis section.

       The out parameter indicates where the compiler's diagnostic output is
       directed.

       The return value is equivalent to the exit value from javac.

       Note that all other classes and methods found in a package whose name
       starts with com.sun.tools.javac (informally known as sub-packages of
       com.sun.tools.javac) are strictly internal and subject to change at any
       time.

EXAMPLES
   Compiling a Simple Program
          One source file, Hello.java, defines a class called greetings.Hello.
          The greetings directory is the package directory both for the source
          file and the class file and is off the current directory. This
          allows us to use the default user class path. It also makes it
          unnecessary to specify a separate destination directory with -d.

             % ls
             greetings/
             % ls greetings
             Hello.java
             % cat greetings/Hello.java
             package greetings;

             public class Hello {
                 public static void main(String[] args) {
                     for (int i=0; i < args.length; i++) {
                         System.out.println("Hello " + args[i]);
                     }
                 }
             }
             % javac greetings/Hello.java
             % ls greetings
             Hello.class   Hello.java
             % java greetings.Hello World Universe Everyone
             Hello World
             Hello Universe
             Hello Everyone


   Compiling Multiple Source Files
          This example compiles all the source files in the package greetings.

             % ls
             greetings/
             % ls greetings
             Aloha.java         GutenTag.java      Hello.java         Hi.java
             % javac greetings/*.java
             % ls greetings
             Aloha.class         GutenTag.class      Hello.class         Hi.class
             Aloha.java          GutenTag.java       Hello.java          Hi.java



   Specifying a User Class Path
          Having changed one of the source files in the previous example, we
          recompile it:

             % pwd
             /examples
             % javac greetings/Hi.java


          Since greetings.Hi refers to other classes in the greetings package,
          the compiler needs to find these other classes. The example above
          works, because our default user class path happens to be the
          directory containing the package directory. But suppose we want to
          recompile this file and not worry about which directory we're in?
          Then we need to add /examples to the user class path. We can do this
          by setting CLASSPATH, but here we'll use the -classpath option.

             % javac -classpath /examples /examples/greetings/Hi.java


          If we change greetings.Hi again, to use a banner utility, that
          utility also needs to be accessible through the user class path.

             % javac -classpath /examples:/lib/Banners.jar \
                                /examples/greetings/Hi.java


          To execute a class in greetings, we need access both to greetings
          and to the classes it uses.

             % java -classpath /examples:/lib/Banners.jar greetings.Hi


   Separating Source Files and Class Files
          It often makes sense to keep source files and class files in
          separate directories, especially on large projects. We use -d to
          indicate the separate class file destination. Since the source files
          are not in the user class path, we use -sourcepath to help the
          compiler find them.

             % ls
             classes/  lib/      src/
             % ls src
             farewells/
             % ls src/farewells
             Base.java      GoodBye.java
             % ls lib
             Banners.jar
             % ls classes
             % javac -sourcepath src -classpath classes:lib/Banners.jar \
               src/farewells/GoodBye.java -d classes
             % ls classes
             farewells/
             % ls classes/farewells
             Base.class      GoodBye.class



          Note:   The compiler compiled src/farewells/Base.java, even though
          we didn't specify it on the command line. To trace automatic
          compiles, use the -verbose option.

   Cross-Compilation Example
          Here we use javac to compile code that will run on a 1.4 VM.

             % javac -target 1.4 -bootclasspath jdk1.4.2/lib/classes.zip \
                     -extdirs "" OldCode.java


          The -target 1.4 option ensures that the generated class files will
          be compatible with 1.4 VMs. By default, javac compiles for JDK 6.

          The Java Platform JDK's javac would also by default compile against
          its own bootstrap classes, so we need to tell javac to compile
          against JDK 1.4 bootstrap classes instead. We do this with
          -bootclasspath and -extdirs. Failing to do this might allow
          compilation against a Java Platform API that would not be present on
          a 1.4 VM and would fail at runtime.

SEE ALSO
          o java - the Java Application Launcher

          o jdb - Java Application Debugger

          o javah - C Header and Stub File Generator

          o javap - Class File Disassembler

          o javadoc - API Documentation Generator

          o jar - JAR Archive Tool

          o The Java Extensions Framework @
            http://java.sun.com/javase/6/docs/technotes/guides/extensions/index.html


                                  07 Aug 2006                         javac(1)
