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javac(1) javac(1)
NAME
javac - Java compiler
SYNOPSIS
javac [ options ] [ sourcefiles ] [ @argfiles ]
PARAMETERS
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 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:
• For a small number of source files, simply list the file names on the command line.
• 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.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; other-wise otherwise
wise the compiler searches the user class path both for class files and source files. You can spec-ify specify
ify different bootstrap or extension classes with the -bootclasspath and -extdirs options; see Cross-Compilation CrossCompilation
Compilation Options below.
A successful type search may produce a class file, a source file, or both. Here is how javac handles
each situation:
• Search produces a class file but no source file: javac uses the class file.
• Search produces a source file but no class file: javac compiles the source file and uses the
resulting class file.
• 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.
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
-classpath classpath
Sets the user class path, overriding the user class path in the CLASSPATH environment vari-able. variable.
able. 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 -depre-cation, -deprecation,
cation, 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:
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:
1.5 The 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 intro-duced introduced
duced after JDK 1.3.
-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, archives,
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 automatic recompilation if their
sources are found.
-verbose
Verbose output. This includes information about each class loaded and each source file com-piled. compiled.
piled.
-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 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 -boot-classpath -bootclasspath
classpath and -extdirs when cross-compiling; see Cross-Compilation Example below.
-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:
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 preveri-fier preverifier
fier 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
-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 appli-cations applications
cations 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 con-tain contain
tain 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 inter-pret interpret
pret 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:
% 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 file-names: filenames:
names: (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
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 des-tination destination
tination 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 the class 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 1.5.
The Java 2 SDk'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 2 Platform API that would not be
present on a 1.4 VM and would fail at runtime.
SEE ALSO
jar(1), java(1), javadoc(1), javah(1), javap(1), jdb(1)
See or search the Java web site for the following:
The Java Extensions Mechanism @
http://java.sun.com/j2se/1.5/docs/guide/extensions/index.html
05 March 2002 javac(1)
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