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javac(1)							      javac(1)



Name
       javac - Java programming language compiler


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




       Arguments may be in any order.


	  options
	     Command-line options.

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

	  classes
	     One  or  more  classes  to	 be processed for annotations (such as
	     MyPackage.MyClass).

	  @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.
       It can also process annotations in Java source files and classes.


       There are two ways to pass source code file names 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).


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
	  -Akey[=value]
	     Options  to  pass	to annotation processors. These are not inter-
	     preted by javac directly, but are made available for use by indi-
	     vidual  processors.  key  should be one or more identifiers sepa-
	     rated by ".".

	  -cp path or -classpath path
	     Specify where to find user class files, and (optionally)  annota-
	     tion  processors  and source files. This class path overrides the
	     user class path in the CLASSPATH environment variable. If neither
	     CLASSPATH,	 -cp  nor -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 also searched for source files.
	     If the -processorpath option is not specified, the class path  is
	     also searched for annotation processors.

	  -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 directory must
	     already exist; javac will not create it. 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 each class files in the same
	     directory as the source file from which it was generated.
	     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  a  summary  of  the
	     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.

	  -endorseddirs directories
	     Override the location of endorsed standards path.

	  -extdirs directories
	     Overrides the location of	the  ext  directory.  The  directories
	     variable  is  a  colon-separated  list  of	 directories. Each JAR
	     archive in the specified directories is searched for class files.
	     All  JAR archives found are automatically part of the class path.
	     If you are cross-compiling (compiling classes  against  bootstrap
	     and  extension  classes  of a different Java platform implementa-
	     tion), this option specifies the  directories  that  contain  the
	     extension	classes. See Cross-Compilation Options for more infor-
	     mation.

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

	  -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.

	  -implicit:{class,none}
	     Controls  the  generation	of  class  files for implicitly loaded
	     source  files.  To	 automatically	generate  class	  files,   use
	     -implicit:class.	To   suppress	class	file  generation,  use
	     -implicit:none. If this option is not specified, the  default  is
	     to automatically generate class files. In this case, the compiler
	     will issue a warning if any such class files are  generated  when
	     also  doing annotation processing. The warning will not be issued
	     if this option is set explicitly. See Searching For Types.

	  -Joption
	     Pass option to the java launcher called by	 javac.	 For  example,
	     -J-Xms48m sets the startup memory to 48 megabytes. 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	imple-
	     mentation	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.

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

	  -proc: {none,only}
	     Controls whether  annotation  processing  and/or  compilation  is
	     done. -proc:none means that compilation takes place without anno-
	     tation processing. -proc:only means that only annotation process-
	     ing is done, without any subsequent compilation.

	  -processor class1[,class2,class3...]
	     Names  of	the  annotation	 processors  to run. This bypasses the
	     default discovery process.

	  -processorpath path
	     Specify where to find annotation processors; if  this  option  is
	     not used, the class path will be searched for processors.

	  -s dir
	     Specify  the directory where to place generated source files. The
	     directory must already exist; javac will  not  create  it.	 If  a
	     class  is part of a package, the compiler puts the source file in
	     a subdirectory reflecting the package name, creating  directories
	     as	 needed.  For  example,	 if you specify -s /home/mysrc and the
	     class is called com.mypackage.MyClass, then the source file  will
	     be placed in /home/mysrc/com/mypackage/MyClass.java.

	  -source release
	     Specifies the version of source code accepted. The following val-
	     ues 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  lan-
		guage features introduced in JDK 5.

	     5	Synonym for 1.5.

	     1.6
		This is the default value. No language changes were introduced
		in Java SE 6. However, encoding errors in source files are now
		reported as errors, instead of warnings, as previously.

	     6	Synonym for 1.6.

	     1.7
		The compiler accepts code with features introduced in JDK 7.

	     7	Synonym for 1.7.

	  -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  class path may be subject to
	     automatic recompilation if their  sources	are  also  found.  See
	     Searching For Types.

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

	  -version
	     Print version information.

	  -Werror
	     Terminate compilation if warnings occur.

	  -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 sup-
       ports 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  ver-
	     sions,  but  not on earlier versions of the VM. Valid targets are
	     1.1 1.2 1.3 1.4 1.5 (also 5) 1.6 (also 6) and 1.7 (also 7).
	     The default for -target depends on the value of -source:

	     o If -source is not specified, the value of -target is 1.7

	     o If -source is 1.2, the value of -target is 1.4

	     o If -source is 1.3, the value of -target is 1.4

	     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.



   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,	 enabling  all
	     available warnings is recommended.

	  -Xlint:all
	     Enable  all  recommended  warnings. In this release, enabling all
	     available warnings is recommended.

	  -Xlint:none
	     Disable all warnings.

	  -Xlint:name
	     Enable warning name. See the section Warnings That Can Be Enabled
	     or	 Disabled  with	 -Xlint	 Option for a list of warnings you can
	     enable with this option.

	  -Xlint:-name
	     Disable warning name.  See	 the  section  Warnings	 That  Can  Be
	     Enabled or Disabled with -Xlint Option for a list of warnings you
	     can disable with this option.

	  -Xmaxerrs 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.

	  -Xprefer:{newer,source}
	     Specify which file to read when both a source file and class file
	     are found for a  type.  (See  Searching  For  Types).  If	-Xpre-
	     fer:newer is used, it reads the newer of the source or class file
	     for a type (default). If the -Xprefer:source option is  used,  it
	     reads  source  file. Use -Xprefer:source when you want to be sure
	     that any annotation processors can	 access	 annotations  declared
	     with a retention policy of SOURCE.

	  -Xpkginfo:{always,legacy,nonempty}
	     Specify handling of package-info files

	  -Xprint
	     Print out textual representation of specified types for debugging
	     purposes; perform neither annotation processing nor  compilation.
	     The format of the output may change.

	  -XprintProcessorInfo
	     Print information about which annotations a processor is asked to
	     process.

	  -XprintRounds
	     Print information about initial and  subsequent  annotation  pro-
	     cessing rounds.



   Warnings That Can Be Enabled or Disabled with -Xlint Option
       Enable  warning	name with the option -Xlint:name, where name is one of
       the following warning names. Similarly, you can	disable	 warning  name
       with the option -Xlint:-name:


	  cast
	     Warn about unnecessary and redundant casts. For example:

	     String s = (String)"Hello!"


	  classfile
	     Warn about issues related to classfile contents.

	  deprecation
	     Warn about use of deprecated items. For example:

		 java.util.Date myDate = new java.util.Date();
		 int currentDay = myDate.getDay();

	     The  method  java.util.Date.getDay	 has been deprecated since JDK
	     1.1.

	  dep-ann
	     Warn about items that are documented with an @deprecated  Javadoc
	     comment, but do not have a @Deprecated annotation. For example:

	       /**
		* @deprecated As of Java SE 7, replaced by {@link #newMethod()}
		*/

	       public static void deprecatedMethood() { }

	       public static void newMethod() { }


	  divzero
	     Warn about division by constant integer 0. For example:

		 int divideByZero = 42 / 0;


	  empty
	     Warn about empty statements after if statements. For example:

	     class E {
		 void m() {
		     if (true) ;
		 }
	     }


	  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 end
	     with 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.

	  finally
	     Warn about finally clauses that  cannot  complete	normally.  For
	     example:

	       public static int m() {
		 try {
		   throw new NullPointerException();
		 } catch (NullPointerException e) {
		   System.err.println("Caught NullPointerException.");
		   return 1;
		 } finally {
		   return 0;
		 }
	       }

	     The  compiler generates a warning for finally block in this exam-
	     ple. When this method is called, it returns a value of 0, not  1.
	     A finally block always executes when the try block exits. In this
	     example, if control is transferred to the catch, then the	method
	     exits. However, the finally block must be executed, so it is exe-
	     cuted, even though control has already been  transferred  outside
	     the method.

	  options
	     Warn  about  issues  relating to the use of command line options.
	     See Cross-Compilation Example for an  example  of	this  kind  of
	     warning.

	  overrides
	     Warn  about  issues regarding method overrides. For example, con-
	     sider the following two classes:

	     public class ClassWithVarargsMethod {
	       void varargsMethod(String... s) { }
	     }


	     public class ClassWithOverridingMethod extends ClassWithVarargsMethod {
	       @Override
	       void varargsMethod(String[] s) { }
	     }

	     The compiler generates a warning similar to the following:
	     warning: [override] varargsMethod(String[]) in  ClassWithOverrid-
	     ingMethod	 overrides   varargsMethod(String...)	in  ClassWith-
	     VarargsMethod; overriding method is missing '...'
	     When the compiler encounters a varargs method, it translates  the
	     varargs  formal parameter into an array. In the method ClassWith-
	     VarargsMethod.varargsMethod, the compiler translates the  varargs
	     formal  parameter String... s to the formal parameter String[] s,
	     an array, which matches the formal parameter of the method Class-
	     WithOverridingMethod.varargsMethod.  Consequently,	 this  example
	     compiles.

	  path
	     Warn about invalid path elements and nonexistent path directories
	     on	 the  command line (with regards to the class path, the source
	     path, and other paths). Such warnings cannot be  suppressed  with
	     the @SuppressWarnings annotation. For example:

	     javac -Xlint:path -classpath /nonexistentpath Example.java


	  processing
	     Warn  about  issues regarding annotation processing. The compiler
	     generates this warning if you have a class that  has  an  annota-
	     tion, and you use an annotation processor that cannot handle that
	     type of exception. For example, the following is a simple annota-
	     tion processor:
	     Source file AnnoProc.java:

	     import java.util.*;
	     import javax.annotation.processing.*;
	     import javax.lang.model.*;
	     import javax.lang.model.element.*;

	     @SupportedAnnotationTypes("NotAnno")
	     public class AnnoProc extends AbstractProcessor {
		 public boolean process(Set<? extends TypeElement> elems, RoundEnvironment renv) {
		     return true;
		 }

		 public SourceVersion getSupportedSourceVersion() {
		     return SourceVersion.latest();
		 }
	     }

	     Source file AnnosWithoutProcessors.java:

	     @interface Anno { }

	     @Anno
	     class AnnosWithoutProcessors { }

	     The following commands compile the annotation processor AnnoProc,
	     then run  this  annotation	 processor  against  the  source  file
	     AnnosWithoutProcessors.java:

	     % javac AnnoProc.java
	     % javac -cp . -Xlint:processing -processor AnnoProc -proc:only AnnosWithoutProcessors.java

	     When  the	compiler  runs	the  annotation	 processor against the
	     source file AnnosWithoutProcessors.java, it generates the follow-
	     ing warning:
	     warning:  [processing]  No processor claimed any of these annota-
	     tions: Anno
	     To resolve this issue, you can rename the annotation defined  and
	     used in the class AnnosWithoutProcessors from Anno to NotAnno.

	  rawtypes
	     Warn  about  unchecked  operations	 on  raw  types. The following
	     statement generates a rawtypes warning:

	     void countElements(List l) { ... }

	     The following does not generate a rawtypes warning:

	     void countElements(List<?> l) { ... }

	     List is a raw type. However,  List<?>  is	a  unbounded  wildcard
	     parameterized  type.  Because  List is a parameterized interface,
	     you should always specify its type argument. In this example, the
	     List  formal  argument is specified with a unbounded wildcard (?)
	     as its formal type parameter, which means that the	 countElements
	     method can accept any instantiation of the List interface.

	  serial
	     Warn  about  missing serialVersionUID definitions on serializable
	     classes. For example:

	     public class PersistentTime implements Serializable
	     {
	       private Date time;

		public PersistentTime() {
		  time = Calendar.getInstance().getTime();
		}

		public Date getTime() {
		  return time;
		}
	     }

	     The compiler generates the following warning:
	     warning: [serial] serializable class PersistentTime has no	 defi-
	     nition of serialVersionUID
	     If a serializable class does not explicitly declare a field named
	     serialVersionUID, then the serialization runtime will calculate a
	     default  serialVersionUID	value  for that class based on various
	     aspects of the class, as described in the Java Object  Serializa-
	     tion  Specification. However, it is strongly recommended that all
	     serializable classes explicitly declare  serialVersionUID	values
	     because  the  default process of computing serialVersionUID vales
	     is highly sensitive to class details that may vary	 depending  on
	     compiler  implementations,	 and  can  thus	 result	 in unexpected
	     InvalidClassExceptions  during  deserialization.  Therefore,   to
	     guarantee	a  consistent  serialVersionUID value across different
	     Java compiler implementations, a serializable class must  declare
	     an explicit serialVersionUID value.

	  static
	     Warn about issues relating to use of statics. For example:

	     class XLintStatic {
		 static void m1() { }
		 void m2() { this.m1(); }
	     }

	     The compiler generates the following warning:

	     warning: [static] static method should be qualified by type name, XLintStatic, instead of by an expression

	     To	 resolve this issue, you can call the static method m1 as fol-
	     lows:

	     XLintStatic.m1();

	     Alternatively,  you  can  remove  the  static  keyword  from  the
	     declaration of the method m1.

	  try
	     Warn  about  issues  relating  to	use  of	 try blocks, including
	     try-with-resources statements. For example, a warning  is	gener-
	     ated for the following statement because the resource ac declared
	     in the try statement is not used:

	     try ( AutoCloseable ac = getResource() ) {
		 // do nothing
	     }


	  unchecked
	     Give more detail for unchecked conversion warnings that are  man-
	     dated by the Java Language Specification. For example:

		 List l = new ArrayList<Number>();
		 List<String> ls = l;	    // unchecked warning

	     During type erasure, the types ArrayList<Number> and List<String>
	     become ArrayList and List, respectively.
	     The variable ls has the parameterized type List<String>. When the
	     List referenced by l is assigned to ls, the compiler generates an
	     unchecked warning; the compiler is unable to determine at compile
	     time,  and moreover knows that the JVM will not be able to deter-
	     mine at runtime, if l refers to a List<String> type; it does not.
	     Consequently, heap pollution occurs.
	     In detail, a heap pollution situation occurs when the List object
	     l, whose static type is List<Number>, is assigned to another List
	     object,  ls, that has a different static type, List<String>. How-
	     ever, the compiler still allows this assignment.  It  must	 allow
	     this assignment to preserve backwards compatibility with versions
	     of Java SE that do not support generics. Because of type erasure,
	     List<Number> and List<String> both become List. Consequently, the
	     compiler allows the assignment of the object l, which has	a  raw
	     type of List, to the object ls.

	  varargs
	     Warn about unsafe usages of variable arguments (varargs) methods,
	     in particular, those that contain	non-reifiable  arguments.  For
	     example:

	     public class ArrayBuilder {
	       public static <T> void addToList (List<T> listArg, T... elements) {
		 for (T x : elements) {
		   listArg.add(x);
		 }
	       }
	     }

	     The  compiler  generates the following warning for the definition
	     of the method ArrayBuilder.addToList:

	     warning: [varargs] Possible heap pollution from parameterized vararg type T

	     When the compiler encounters a varargs method, it translates  the
	     varargs  formal  parameter	 into an array. However, the Java pro-
	     gramming language does not	 permit	 the  creation	of  arrays  of
	     parameterized  types.  In	the method ArrayBuilder.addToList, the
	     compiler translates the varargs formal parameter T... elements to
	     the  formal parameter T[] elements, an array. However, because of
	     type erasure, the compiler converts the varargs formal  parameter
	     to	 Object[]  elements.  Consequently,  there is a possibility of
	     heap pollution.



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	direc-
       tory,  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:


       % 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



ANNOTATION PROCESSING
       javac  provides	direct	support for annotation processing, superseding
       the need for the separate annotation processing tool, apt.


       The API for annotation  processors  is  defined	in  the	 javax.annota-
       tion.processing and javax.lang.model packages and subpackages.


   Overview of annotation processing
       Unless  annotation  processing  is disabled with the -proc:none option,
       the compiler searches for any annotation processors that are available.
       The  search path can be specified with the -processorpath option; if it
       is not given, the user class path is used. Processors  are  located  by
       means  of  service  provider-configuration  files  named	 META-INF/ser-
       vices/javax.annotation.processing.Processor on the  search  path.  Such
       files should contain the names of any annotation processors to be used,
       listed one per line. Alternatively, processors can be specified explic-
       itly, using the -processor option.


       After  scanning	the  source  files  and classes on the command line to
       determine what annotations are present, the compiler queries  the  pro-
       cessors	to  determine  what  annotations they process. When a match is
       found, the processor will be invoked. A processor may "claim" the anno-
       tations	it processes, in which case no further attempt is made to find
       any processors for those annotations. Once all  annotations  have  been
       claimed, the compiler does not look for additional processors.


       If any processors generate any new source files, another round of anno-
       tation processing will occur: any newly generated source files will  be
       scanned,	 and  the  annotations	processed  as  before.	Any processors
       invoked on previous rounds will	also  be  invoked  on  all  subsequent
       rounds. This continues until no new source files are generated.


       After a round occurs where no new source files are generated, the anno-
       tation processors will be invoked one last time, to give them a	chance
       to  complete  any  work	they  may  need	 to  do.  Finally,  unless the
       -proc:only option is used, the compiler will compile the	 original  and
       all the generated source files.


   Implicitly loaded source files
       To  compile  a set of source files, the compiler may need to implicitly
       load additional source files. (See Searching For Types). Such files are
       currently  not  subject	to annotation processing. By default, the com-
       piler will give a warning if annotation processing has occurred and any
       implicitly  loaded  source files are compiled. See the -implicit option
       for ways to suppress the warning.


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. If both are found, you can use the -Xprefer  option  to  instruct
       the compiler which to use. If newer is given, the compiler will use the
       newer of the two files. If source is given,  it	will  use  the	source
       file. The default is newer.


       If  a  type  search  finds a source file for a required type, either by
       itself, or as a result of the setting for -Xprefer, the	compiler  will
       read  the  source file to get the information it needs. In addition, it
       will by default compile the source  file	 as  well.  You	 can  use  the
       -implicit  option  to  specify the behavior. If none is given, no class
       files will be generated for the source file. If class is	 given,	 class
       files will be generated for the source file.


       The  compiler may not discover the need for some type information until
       after annotation processing is complete. If  the	 type  information  is
       found  in  a source file and no -implicit option is given, the compiler
       will give a warning that the file is being compiled without being  sub-
       ject  to	 annotation processing. To disable the warning, either specify
       the file on the command line (so that it will be subject to  annotation
       processing) or use the -implicit option to specify whether or not class
       files should be generated for such source files.


PROGRAMMATIC INTERFACE
       javac supports the new Java Compiler API defined	 by  the  classes  and
       interfaces in the javax.tools package.


   Example
       To  perform a compilation using arguments as you would give on the com-
       mand line, you can use the following:


       JavaCompiler javac = ToolProvider.getSystemJavaCompiler();
       int rc = javac.run(null, null, null, args);




       This will write any diagnostics to  the	standard  output  stream,  and
       return  the  exit code that javac would give when invoked from the com-
       mand line.


       You can use other methods on the javax.tools.JavaCompiler interface  to
       handle  diagnostics,  control where files are read from and written to,
       and so on.


   Old Interface
       Note: This API is retained for backwards compatibility  only;  all  new
       code should use the Java Compiler API, described above.


       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 1.6 VM.


       % javac -source 1.6 -target 1.6 -bootclasspath jdk1.6.0/lib/rt.jar \
		   -extdirs "" OldCode.java



       The -source 1.6 option specifies that version 1.6 (or 6)	 of  the  Java
       programming  language be used to compile OldCode.java. The option -tar-
       get 1.6 option ensures that the generated class files will be  compati-
       ble  with  1.6  VMs.  Note that in most cases, the value of the -target
       option is the value of the -source option; in  this  example,  you  can
       omit the -target option.


       You  must specify the -bootclasspath option to specify the correct ver-
       sion of the bootstrap classes (the rt.jar library). If  not,  the  com-
       piler generates a warning:


       % javac -source 1.6 OldCode.java
       warning: [options] bootstrap class path not set in conjunction with -source 1.6



       If  you	do  not	 specify the correct version of bootstrap classes, the
       compiler will use the old language rules (in this example, it will  use
       version	1.6  of	 the  Java programming language) combined with the new
       bootstrap classes, which can result in class files that do not work  on
       the  older  platform  (in  this	case,  Java SE 6) because reference to
       non-existent methods can get included.


SEE ALSO
	  o The javac Guide @
	    http://download.oracle.com/javase/7/docs/tech-
	    notes/guides/javac/index.html

	  o java(1) - the Java Application Launcher

	  o jdb(1) - Java Application Debugger

	  o javah(1) - C Header and Stub File Generator

	  o javap(1) - Class File Disassembler

	  o javadoc(1) - API Documentation Generator

	  o jar(1) - JAR Archive Tool

	  o The Java Extensions Framework @
	    http://download.oracle.com/javase/7/docs/technotes/guides/extensions/index.html






				  10 May 2011			      javac(1)
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