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.
add an example, a script, a trick and tips
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.
source
javac Client.java
javac Test_Client.java
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).
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.
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.
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.
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