javac - Unix, Linux Command
NAME
javac - Java compiler
SYNOPSIS
javac [
options ]
[
sourcefiles ]
[
@argfiles ]
PARAMETERS
Arguments may be in any order.
Tag | Description |
options |
Command line options.
|
sourcefiles |
One or more source files to be compiled (such as
MyClass.java).
|
@argfiles
|
One or more files that list 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 file names to
javac:
Tag | Description |
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 Applets ancestor classes:
java.awt.Panel, java.awt.Container, java.awt.Component, and
java.awt.Object.
When the compiler needs type information, it looks for a source
file or class file which defines the type.
The compiler searches
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 use the
-sourcepath option, the compiler
searches the indicated path for source files; otherwise the
compiler searches the user class path both for 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:
Tag | Description |
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.
By default,
javac considers a class file out of date only if
it is older than the source file.
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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 implementation and are
subject to change in the future.
Non-standard options begin with
-X. Standard Options
Tag | Description |
-classpath classpath | |
Sets 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.
|
-Djava.ext.dirs=directories | |
Override the location of installed extensions.
|
-Djava.endorsed.dirs=directories | |
Override the location of endorsed standards path.
|
-d directory | |
Sets 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 | |
Shows 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 | |
Sets the source file encoding name, such as EUCJIS/SJIS/ISO8859-1/UTF8.
If
-encoding is not specified, the platform default converter is
used.
|
-g |
Generates all debugging information, including local variables.
By default, only line number and source file
information is generated.
|
-g:none |
Does not generate any debugging information.
|
-g:keyword-list | |
Generates only some kinds of debugging information, specified
by a comma separated list of keywords. Valid keywords are:
Tag | Description |
source |
Source file debugging information
|
lines |
Line number debugging information
|
vars |
Local variable debugging information
|
|
-help |
Prints a synopsis of standard options.
|
-nowarn |
Disables warning messages. This has the same
meaning as
-Xlint:none. |
-source release | |
Enables support for compiling source code containing assertions.
The following values for
release are allowed:
|
Tag | Description |
1.5
|
he compiler accepts code containing generics and other
language features introduced in JDK 1.5. The compiler
defaults to the 1.5 behavior if the -source flag
is not used.
|
5
|
Synonym for 1.5
|
1.4
|
the compiler accepts code containing assertions, which
were introduced in JDK 1.4.
|
1.3
|
the compiler does not support assertions, generics, or
other language features introduced after JDK 1.3.
|
Tag | Description |
-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.
Tag | Description |
-verbose |
Verbose output.
This includes information about each class
loaded and each source file compiled.
|
-X |
Display information about non-standard options and exit.
|
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Cross-Compilation Options
By default, classes are compiled against the bootstrap and
extension classes of the JDK 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.
Tag | Description |
-target version | |
Generates class files that will work on
VMs with the specified version.
The default is to generate class files to be
compatible with 1.2
VMs, with one exception. When the -source 1.4 option is used, the default target is 1.4.
The versions supported by javac are:
Tag | Description |
1.1
|
Ensures that generated class files will be compatible
with 1.1 and later.
VMs. |
1.2
|
Generates class files that will run on 1.2 and later
VMs, but will not run on 1.1
VMs. |
1.3
|
Generates class files that run on
VMs in the Java 2 SDK, v1.3 and later, but
will not run on 1.1 or 1.2
VMs. |
1.4
|
Generates class files that will run on VMs
in JDK 1.4 and later, but will not run on 1.1, 1.2, or 1.3 VMs.
|
1.5
|
Generate class files that are compatible only with JDK 1.5 VMs.
|
5
|
Synonym for 1.5
|
|
-bootclasspath bootclasspath | |
Cross-compiles 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.
|
-cldc1.0 |
Use to compile CLDC programs. The compiler generates stack
maps making the use of the preverifier unnecessary.
|
-extdirs directories | |
Cross-compiles against the specified extension directories.
Directories are a colon-separated list of directories.
Each
JAR archive in the specified directories is searched for class files.
|
Non-Standard Options
Tag | Description |
-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.
|
-lint: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
Tag | Description |
-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.
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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. 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. 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.
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:
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
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Tag | Description |
Create a file named
| |
classes containing:
MyClass1.java
MyClass2.java
MyClass3.java
|
|
You would then run javac with:
|
|
% javac @options @classes
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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
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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
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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
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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
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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
were in?
Then we need to add
/examples to the user class path.
We can do this by setting CLASSPATH, but here well use the
-classpath option.
% javac -classpath \examples /examples/greetings/Hi.java
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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
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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
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Note: The compiler compiled src/farewells/Base.java, even
though we didnt 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
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The
-target 1.4 option ensures that the generated class files will
be compatible with 1.4
VMs. BY default,
javac compiles for 1.5.
The Java 2 SDks
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 2 Platform
API that would not be present on a 1.4
VM and would fail at runtime.
SEE ALSO
See or search the Java web site for the following:
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