man.txt

javac(1)                                                                                                                                        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 directo‐
                ries 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  sepa‐
                rated  by  colons (:) and can be directories, JAR archives, or ZIP archives. If packages are used, the local path name within the direc‐
                tory 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  new‐
       line-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  spec‐
          ify 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)