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javac(1) Basic Tools javac(1)
NAME
javac - Reads Java class and interface definitions and compiles them into bytecode and class files.
SYNOPSIS
javac [ options ] [ sourcefiles ] [ classes] [ @argfiles ]
Arguments can be in any order:
options
Command-line options. See 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 list options and source files. The -J options are not allowed in these files. See
Command-Line Argument Files.
DESCRIPTION
The javac command reads class and interface definitions, written in the Java programming language, and compiles
them into bytecode class files. The javac command can also process annotations in Java source files and classes.
There are two ways to pass source code file names to javac.
• For a small number of source files, list the file names on the command line.
• For a large number of source files, list the file names in a file that is separated by blanks or line breaks. Use
the list file name preceded by an at sign (@) with the javac command.
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 that combine the inner and
outer class names, such as MyClass$MyInnerClass.class.
Arrange source files in a directory tree that reflects their package tree. For example, if all of your source files
are in /workspace, then put the source code for com.mysoft.mypack.MyClass 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 the -d option.
OPTIONS
The compiler has a set of standard options that are supported on the current development environment. An additional
set of nonstandard options are specific to the current virtual machine and compiler implementations and are subject
to change in the future. Nonstandard options begin with the -X option.
• See also Cross-Compilation Options
• See also Nonstandard Options
STANDARD OPTIONS
-Akey[=value]
Specifies options to pass to annotation processors. These options are not interpreted by javac directly, but
are made available for use by individual processors. The key value should be one or more identifiers
separated by a dot (.).
-cp path or -classpath path
Specifies where to find user class files, and (optionally) annotation 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, then the user class path is the current directory. See Setting the Class Path.
If the -sourcepath option is not specified, then the user class path is also searched for source files.
If the -processorpath option is not specified, then the class path is also searched for annotation
processors.
-Djava.ext.dirs=directories
Overrides the location of installed extensions.
-Djava.endorsed.dirs=directories
Overrides the location of the endorsed standards path.
-d directory
Sets the destination directory for class files. The directory must already exist because javac does not
create it. If a class is part of a package, then javac puts the class file in a subdirectory that reflects
the package name and creates directories as needed.
If you specify -d/home/myclasses and the class is called com.mypackage.MyClass, then the class file is
/home/myclasses/com/mypackage/MyClass.class.
If the -d option is not specified, then javac puts each class file in the same directory as the source file
from which it was generated.
Note: The directory specified by the -d option 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 the -deprecation
option, javac shows a summary of the source files that use or override deprecated members or classes. The
-deprecation option is shorthand for -Xlint:deprecation.
-encoding encoding
Sets the source file encoding name, such as EUC-JP and UTF-8. If the -encoding option is not specified, then
the platform default converter is used.
-endorseddirs directories
Overrides the location of the endorsed standards path.
-extdirs directories
Overrides the location of the ext directory. The directories variable is a colon-separated list of
directories. Each JAR file in the specified directories is searched for class files. All JAR files found
become part of the class path.
If you are cross-compiling (compiling classes against bootstrap and extension classes of a different Java
platform implementation), then this option specifies the directories that contain the extension classes. See
Cross-Compilation Options for more information.
-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.
-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, then the default is to automatically generate class files. In this case, the compiler issues a
warning if any such class files are generated when also doing annotation processing. The warning is not
issued when the -implicit option is set explicitly. See Searching for Types.
-Joption
Passes option to the Java Virtual Machine (JVM), where option is one of the options described on the
reference page for the Java launcher. For example, -J-Xms48m sets the startup memory to 48 MB. See java(1).
Note: The CLASSPATH, -classpath, -bootclasspath, and -extdirs options do not specify the classes used to run
javac. Trying to customize the compiler implementation with these options and variables is risky and often
does not accomplish what you want. If you must customize the complier implementation, then use the -J option
to pass options through to the underlying Java launcher.
-nowarn
Disables warning messages. This option operates the same as the -Xlint:none option.
-parameters
Stores formal parameter names of constructors and methods in the generated class file so that the method
java.lang.reflect.Executable.getParameters from the Reflection API can retrieve them.
-proc: [none, only]
Controls whether annotation processing and compilation are done. -proc:none means that compilation takes
place without annotation processing. -proc:only means that only annotation processing 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
Specifies where to find annotation processors. If this option is not used, then the class path is searched
for processors.
-s dir
Specifies the directory where to place the generated source files. The directory must already exist because
javac does not create it. If a class is part of a package, then the compiler puts the source file in a
subdirectory that reflects the package name and creates directories as needed.
If you specify -s /home/mysrc and the class is called com.mypackage.MyClass, then the source file is put in
/home/mysrc/com/mypackage/MyClass.java.
-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 Java
SE 1.3.
1.4 The compiler accepts code containing assertions, which were introduced in Java SE 1.4.
1.5 The compiler accepts code containing generics and other language features introduced in Java SE 5.
5 Synonym for 1.5.
1.6 No language changes were introduced in Java SE 6. However, encoding errors in source files are now
reported as errors instead of warnings as in earlier releases of Java Platform, Standard Edition.
6 Synonym for 1.6.
1.7 The compiler accepts code with features introduced in Java SE 7.
7 Synonym for 1.7.
1.8 This is the default value. The compiler accepts code with features introduced in Java SE 8.
8 Synonym for 1.8.
-sourcepath sourcepath
Specifies the source code path to search for class or interface definitions. As with the user class path,
source path entries are separated by colons (:) on Oracle Solaris and semicolons on Windows and can be
directories, JAR archives, or ZIP archives. If packages are used, then the local path name within the
directory or archive must reflect the package name.
Note: Classes found through the class path might be recompiled when their source files are also found. See
Searching for Types.
-verbose
Uses verbose output, which includes information about each class loaded and each source file compiled.
-version
Prints release information.
-werror
Terminates compilation when warnings occur.
-X
Displays information about nonstandard options and exits.
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 the -bootclasspath and -extdirs options when
cross-compiling.
-target version
Generates class files that target a specified release of the virtual machine. Class files will run on the
specified target and on later releases, but not on earlier releases of the JVM. Valid targets are 1.1, 1.2,
1.3, 1.4, 1.5 (also 5), 1.6 (also 6), 1.7 (also 7), and 1.8 (also 8).
The default for the -target option depends on the value of the -source option:
• If the -source option is not specified, then the value of the -target option is 1.8
• If the -source option is 1.2, then the value of the -target option is 1.4
• If the -source option is 1.3, then the value of the -target option is 1.4
• If the -source option is 1.5, then the value of the -target option is 1.8
• If the -source option is 1.6, then the value of the -target is option 1.8
• If the -source option is 1.7, then the value of the -target is option 1.8
• For all other values of the -source option, the value of the -target option is the value of the -source
option.
-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.
COMPACT PROFILE OPTION
Beginning with JDK 8, the javac compiler supports compact profiles. With compact profiles, applications that do not
require the entire Java platform can be deployed and run with a smaller footprint. The compact profiles feature
could be used to shorten the download time for applications from app stores. This feature makes for more compact
deployment of Java applications that bundle the JRE. This feature is also useful in small devices.
The supported profile values are compact1, compact2, and compact3. These are additive layers. Each higher-numbered
compact profile contains all of the APIs in profiles with smaller number names.
-profile
When using compact profiles, this option specifies the profile name when compiling. For example:
javac -profile compact1 Hello.java
javac does not compile source code that uses any Java SE APIs that is not in the specified profile. Here is
an example of the error message that results from attempting to compile such source code:
cd jdk1.8.0/bin
./javac -profile compact1 Paint.java
Paint.java:5: error: Applet is not available in profile 'compact1'
import java.applet.Applet;
In this example, you can correct the error by modifying the source to not use the Applet class. You could
also correct the error by compiling without the -profile option. Then the compilation would be run against
the full set of Java SE APIs. (None of the compact profiles include the Applet class.)
An alternative way to compile with compact profiles is to use the -bootclasspath option to specify a path to
an rt.jar file that specifies a profile's image. Using the -profile option instead does not require a
profile image to be present on the system at compile time. This is useful when cross-compiling.
NONSTANDARD OPTIONS
-Xbootclasspath/p:path
Adds a suffix to the bootstrap class path.
-Xbootclasspath/a:path
Adds a prefix to the bootstrap class path.
-Xbootclasspath/:path
Overrides the location of the bootstrap class files.
-Xdoclint:[-]group [/access]
Enables or disables specific groups of checks, where group is one of the following values: accessibility,
syntax, reference, html or missing. For more information about these groups of checks see the -Xdoclint
option of the javadoc command. The -Xdoclint option is disabled by default in the javac command.
The variable access specifies the minimum visibility level of classes and members that the -Xdoclint option
checks. It can have one of the following values (in order of most to least visible) : public, protected,
package and private. For example, the following option checks classes and members (with all groups of
checks) that have the access level protected and higher (which includes protected, package and public):
-Xdoclint:all/protected
The following option enables all groups of checks for all access levels, except it will not check for HTML
errors for classes and members that have access level package and higher (which includes package and
public):
-Xdoclint:all,-html/package
-Xdoclint:none
Disables all groups of checks.
-Xdoclint:all[/access]
Enables all groups of checks.
-Xlint
Enables all recommended warnings. In this release, enabling all available warnings is recommended.
-Xlint:all
Enables all recommended warnings. In this release, enabling all available warnings is recommended.
-Xlint:none
Disables all warnings.
-Xlint:name
Disables warning name. See Enable or Disable Warnings with the -Xlint Option for a list of warnings you can
disable with this option.
-Xlint:-name
Disables warning name. See Enable or Disable Warnings with the -Xlint Option with the -Xlint option to get a
list of warnings that you can disable with this option.
-Xmaxerrs number
Sets the maximum number of errors to print.
-Xmaxwarns number
Sets the maximum number of warnings to print.
-Xstdout filename
Sends compiler messages to the named file. By default, compiler messages go to System.err.
-Xprefer:[newer,source]
Specifies which file to read when both a source file and class file are found for a type. (See Searching for
Types). If the -Xprefer:newer option is used, then it reads the newer of the source or class file for a type
(default). If the -Xprefer:source option is used, then it reads the 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]
Control whether javac generates package-info.class files from package-info.java files. Possible mode
arguments for this option include the following.
always Always generate a package-info.class file for every package-info.java file. This option may be useful
if you use a build system such as Ant, which checks that each .java file has a corresponding .class
file.
legacy Generate a package-info.class file only if package-info.java contains annotations. Don't generate a
package-info.class file if package-info.java only contains comments.
Note: A package-info.class file might be generated but be empty if all the annotations in the
package-info.java file have RetentionPolicy.SOURCE.
nonempty
Generate a package-info.class file only if package-info.java contains annotations with
RetentionPolicy.CLASS or RetentionPolicy.RUNTIME.
-Xprint
Prints a textual representation of specified types for debugging purposes. Perform neither annotation
processing nor compilation. The format of the output could change.
-XprintProcessorInfo
Prints information about which annotations a processor is asked to process.
-XprintRounds
Prints information about initial and subsequent annotation processing rounds.
ENABLE OR DISABLE WARNINGS WITH THE -XLINT OPTION
Enable warning name with the -Xlint:name option, where name is one of the following warning names. Note that you
can disable a warning with the -Xlint:-name: option.
cast Warns about unnecessary and redundant casts, for example:
String s = (String) "Hello!"
classfile
Warns about issues related to class file contents.
deprecation
Warns about the 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
Warns 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
Warns about division by the constant integer 0, for example:
int divideByZero = 42 / 0;
empty Warns about empty statements after ifstatements, for example:
class E {
void m() {
if (true) ;
}
}
fallthrough
Checks the switch blocks for fall-through cases and provides 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 option was used when compiling this code, then the compiler emits a warning about
possible fall-through into case, with the line number of the case in question.
finally
Warns about finally clauses that cannot complete normally, for example:
public static int m() {
try {
throw new NullPointerException();
} catch (NullPointerException(); {
System.err.println("Caught NullPointerException.");
return 1;
} finally {
return 0;
}
}
The compiler generates a warning for the finally block in this example. When the int method is called, it
returns a value of 0. A finally block executes when the try block exits. In this example, when control is
transferred to the catch block, the int method exits. However, the finally block must execute, so it is
executed, even though control was transferred outside the method.
options
Warns about issues that related to the use of command-line options. See Cross-Compilation Options.
overrides
Warns about issues regarding method overrides. For example, consider 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 ClassWithOverridingMethod
overrides varargsMethod(String...) in ClassWithVarargsMethod; overriding
method is missing '...'
When the compiler encounters a varargs method, it translates the varargs formal parameter into an array. In
the method ClassWithVarargsMethod.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
ClassWithOverridingMethod.varargsMethod. Consequently, this example compiles.
path Warns about invalid path elements and nonexistent path directories on the command line (with regard 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 when you have a class
that has an annotation, and you use an annotation processor that cannot handle that type of exception. For
example, the following is a simple annotation processor:
Source file AnnocProc.java:
import java.util.*;
import javax.annotation.processing.*;
import javax.lang.model.*;
import.javaz.lang.model.element.*;
@SupportedAnnotationTypes("NotAnno")
public class AnnoProc extends AbstractProcessor {
public boolean process(Set 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 following warning:
warning: [processing] No processor claimed any of these annotations: Anno
To resolve this issue, you can rename the annotation defined and used in the class AnnosWithoutProcessors
from Anno to NotAnno.
rawtypes
Warns about unchecked operations on raw types. The following statement generates a rawtypes warning:
void countElements(List l) { ... }
The following example does not generate a rawtypes warning
void countElements(List l) { ... }
List is a raw type. However, List is an unbounded wildcard parameterized type. Because List is a
parameterized interface, always specify its type argument. In this example, the List formal argument is
specified with an unbounded wildcard (?) as its formal type parameter, which means that the countElements
method can accept any instantiation of the List interface.
Serial Warns 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 definition of
serialVersionUID
If a serializable class does not explicitly declare a field named serialVersionUID, then the serialization
runtime environment calculates a default serialVersionUID value for that class based on various aspects of
the class, as described in the Java Object Serialization 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 can vary depending on compiler
implementations, and as a result, might cause an unexpected InvalidClassExceptions during deserialization.
To guarantee a consistent serialVersionUID value across different Java compiler implementations, a
serializable class must declare an explicit serialVersionUID value.
static Warns about issues relating to the 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 follows:
XLintStatic.m1();
Alternately, you can remove the static keyword from the declaration of the method m1.
try Warns about issues relating to use of try blocks, including try-with-resources statements. For example, a
warning is generated for the following statement because the resource ac declared in the try block is not
used:
try ( AutoCloseable ac = getResource() ) { // do nothing}
unchecked
Gives more detail for unchecked conversion warnings that are mandated by the Java Language Specification,
for example:
List l = new ArrayList();
List ls = l; // unchecked warning
During type erasure, the types ArrayList and List become ArrayList and List, respectively.
The ls command has the parameterized type List. When the List referenced by l is assigned to ls, the
compiler generates an unchecked warning. At compile time, the compiler and JVM cannot determine whether l
refers to a List type. In this case, l does not refer to a List type. As a result, heap
pollution occurs.
A heap pollution situation occurs when the List object l, whose static type is List, is assigned to
another List object, ls, that has a different static type, List. However, the compiler still allows
this assignment. It must allow this assignment to preserve backward compatibility with releases of Java SE
that do not support generics. Because of type erasure, List and List 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
Warns about unsafe usages of variable arguments (varargs) methods, in particular, those that contain non-
reifiable arguments, for example:
public class ArrayBuilder {
public static void addToList (List listArg, T... elements) {
for (T x : elements) {
listArg.add(x);
}
}
}
Note: A non-reifiable type is a type whose type information is not fully available at runtime.
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 programming 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, you can specify one or more files that 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 file names in any combination. The arguments within a file
can be separated by spaces or new line characters. If a file name contains embedded spaces, then put the whole file
name in double quotation marks.
File Names within an argument file are relative to the current directory, not the location of the argument file.
Wild cards (*) are not allowed in these lists (such as for specifying *.java). Use of the at sign (@) 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 the javac command, pass in the path and name of each argument file with the at sign (@) leading
character. When the javac command encounters an argument beginning with the at sign (@), it expands the contents of
that file into the argument list.
Example 1 Single Argument 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 Example 2
Example 2 Two Argument Files
You can create two argument files: one for the javac options and the other for the source file names. Note that the
following lists have no line-continuation characters.
Create a file named options that contains the following:
-d classes
-g
-sourcepath /java/pubs/ws/1.3/src/share/classes
Create a file named classes that contains the following:
MyClass1.java
MyClass2.java
MyClass3.java
Then, run the javac command as follows:
javac @options @classes
Example 3 Argument Files with Paths
The argument files can have paths, but any file names inside the files are relative to the current working
directory (not path1 or path2):
javac @path1/options @path2/classes
ANNOTATION PROCESSING
The javac command provides direct support for annotation processing, superseding the need for the separate
annotation processing command, apt.
The API for annotation processors is defined in the javax.annotation.processing and javax.lang.model packages and
subpackages.
HOW ANNOTATION PROCESSING WORKS
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 no path is
specified, then the user class path is used. Processors are located by means of service provider-configuration
files named META-INF/services/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
explicitly, 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 processors to determine what annotations they process. When a match is found, the processor is
called. A processor can claim the annotations it processes, in which case no further attempt is made to find any
processors for those annotations. After all of the annotations are claimed, the compiler does not search for
additional processors.
If any processors generate new source files, then another round of annotation processing occurs: Any newly
generated source files are scanned, and the annotations processed as before. Any processors called on previous
rounds are also called 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 annotation processors are called one last time,
to give them a chance to complete any remaining work. Finally, unless the -proc:only option is used, the compiler
compiles the original and all generated source files.
IMPLICITLY LOADED SOURCE FILES
To compile a set of source files, the compiler might need to implicitly load additional source files. See Searching
for Types. Such files are currently not subject to annotation processing. By default, the compiler gives a warning
when annotation processing occurred and any implicitly loaded source files are compiled. The -implicit option
provides a way to suppress the warning.
SEARCHING FOR TYPES
To compile a source file, the compiler often needs information about a type, but the type definition is not in the
source files specified 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 that provide information through inheritance.
For example, when you create a subclass java.applet.Applet, you are also using the ancestor classes of Applet:
java.awt.Panel, java.awt.Container, java.awt.Component, and java.lang.Object.
When the compiler needs type information, it searches for a source file or class file that 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 option.
If you set the -sourcepath option, then 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 the -extdirs options. See
Cross-Compilation Options.
A successful type search may produce a class file, a source file, or both. If both are found, then you can use the
-Xprefer option to instruct the compiler which to use. If newer is specified, then the compiler uses the newer of
the two files. If source is specified, the compiler uses 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 the
-Xprefer option, then the compiler reads the source file to get the information it needs. By default the compiler
also compiles the source file. You can use the -implicit option to specify the behavior. If none is specified, then
no class files are generated for the source file. If class is specified, then class files are generated for the
source file.
The compiler might not discover the need for some type information until after annotation processing completes.
When the type information is found in a source file and no -implicit option is specified, the compiler gives a
warning that the file is being compiled without being subject 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
The javac command supports the new Java Compiler API defined by the classes and interfaces in the javax.tools
package.
EXAMPLE
To compile as though providing command-line arguments, use the following syntax:
JavaCompiler javac = ToolProvider.getSystemJavaCompiler();
The example writes diagnostics to the standard output stream and returns the exit code that javac would give when
called from the command line.
You can use other methods in the javax.tools.JavaCompiler interface to handle diagnostics, control where files are
read from and written to, and more.
OLD INTERFACE
Note: This API is retained for backward compatibility only. All new code should use the newer Java Compiler API.
The com.sun.tools.javac.Main class provides two static methods to call 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 typically be passed to the compiler.
The out parameter indicates where the compiler diagnostic output is directed.
The return value is equivalent to the exit value from javac.
Note: All other classes and methods found in a package with names that start with com.sun.tools.javac (subpackages
of com.sun.tools.javac) are strictly internal and subject to change at any time.
EXAMPLES
Example 1 Compile a Simple Program
This example shows how to compile the Hello.java source file in the greetings directory. The class defined in
Hello.java is called greetings.Hello. The greetings directory is the package directory both for the source file and
the class file and is underneath the current directory. This makes it possible to use the default user class path.
It also makes it unnecessary to specify a separate destination directory with the -d option.
The source code in 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]);
}
}
}
Compile greetings.Hello:
javac greetings/Hello.java
Run greetings.Hello:
java greetings.Hello World Universe Everyone
Hello World
Hello Universe
Hello Everyone
Example 2 Compile Multiple Source Files
This example compiles the Aloha.java, GutenTag.java, Hello.java, and Hi.java source files in the greetings package.
% javac greetings/*.java
% ls greetings
Aloha.class GutenTag.class Hello.class Hi.class
Aloha.java GutenTag.java Hello.java Hi.java
Example 3 Specify a User Class Path
After changing one of the source files in the previous example, recompile it:
pwd
/examples
javac greetings/Hi.java
Because greetings.Hi refers to other classes in the greetings package, the compiler needs to find these other
classes. The previous example works because the default user class path is the directory that contains the package
directory. If you want to recompile this file without concern for which directory you are in, then add the examples
directory to the user class path by setting CLASSPATH. This example uses the -classpath option.
javac -classpath /examples /examples/greetings/Hi.java
If you change greetings.Hi to use a banner utility, then 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 the greetings package, the program needs access to the greetings package, and to the classes
that the greetings classes use.
java -classpath /examples:/lib/Banners.jar greetings.Hi
Example 4 Separate Source Files and Class Files
The following example uses javac to compile code that runs on JVM 1.7.
javac -source 1.7 -target 1.7 -bootclasspath jdk1.7.0/lib/rt.jar \
-extdirs "" OldCode.java
The -source 1.7 option specifies that release 1.7 (or 7) of the Java programming language be used to compile
OldCode.java. The option -target 1.7 option ensures that the generated class files are compatible with JVM 1.7.
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 version of the bootstrap classes (the rt.jar
library). If not, then the compiler generates a warning:
javac -source 1.7 OldCode.java
warning: [options] bootstrap class path not set in conjunction with
-source 1.7
If you do not specify the correct version of bootstrap classes, then the compiler uses the old language rules (in
this example, it uses version 1.7 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 7) because reference to
nonexistent methods can get included.
Example 5 Cross Compile
This example uses javac to compile code that runs on JVM 1.7.
javac -source 1.7 -target 1.7 -bootclasspath jdk1.7.0/lib/rt.jar \
-extdirs "" OldCode.java
The-source 1.7 option specifies that release 1.7 (or 7) of the Java programming language to be used to compile
OldCode.java. The -target 1.7 option ensures that the generated class files are compatible with JVM 1.7.
You must specify the -bootclasspath option to specify the correct version of the bootstrap classes (the rt.jar
library). If not, then the compiler generates a warning:
javac -source 1.7 OldCode.java
warning: [options] bootstrap class path not set in conjunction with -source 1.7
If you do not specify the correct version of bootstrap classes, then the compiler uses the old language rules
combined with the new bootstrap classes. This combination can result in class files that do not work on the older
platform (in this case, Java SE 7) because reference to nonexistent methods can get included. In this example, the
compiler uses release 1.7 of the Java programming language.
SEE ALSO
• java(1)
• jdb(1)
• javadoc(1)
• jar(1)
• jdb(1)
JDK 8 03 March 2015 javac(1)