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 deter-
mines 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 base-
name 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 invoca-
tions).
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 class-
path 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 Sys-
tem.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 desti-
nation 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/mypack-
age/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 ar-
chives, 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 auto-
matic 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 sup-
ports cross-compiling, where classes are compiled against a boot-
strap and extension classes of a different Java platform implementa-
tion. 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 sepa-
rated 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 avail-
able warnings are recommended.
-Xlint:none
Disable all warnings not mandated by the Java Language Speci-
fication.
-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 serializ-
able classes.
-Xlint:finally
Warn about finally clauses that cannot complete normally.
-Xlint:fallthrough
Check switch blocks for fall-through cases and provide a warn-
ing 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 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:
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 direc-
tory containing the package directory. But suppose we want to recom-
pile 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 set-
ting 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 util-
ity 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 sepa-
rate directories, especially on large projects. We use -d to indi-
cate 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 com-
piles, 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 -boot-
classpath 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/exten-
sions/index.html
07 Aug 2006 javac(1)