Javac

Description

Compiles a Java source tree.

The source and destination directory will be recursively scanned for Java source files to compile. Only .java files that have no corresponding .class file or where the .class file is older than the .java file will be compiled.

Note: Apache Ant uses only the names of the source and class files to find the classes that need a rebuild. It will not scan the source and therefore will have no knowledge about nested classes, classes that are named differently from the source file, and so on. See the <depend> task for dependency checking based on other than just existence/modification times.

When the source files are part of a package, the directory structure of the source tree should follow the package hierarchy.

It is possible to refine the set of files that are being compiled. This can be done with the includes, includesfile, excludes, and excludesfile attributes. With the includes or includesfile attribute, you specify the files you want to have included. The exclude or excludesfile attribute is used to specify the files you want to have excluded. In both cases, the list of files can be specified by either the filename, relative to the directory(s) specified in the srcdir attribute or nested <src> element(s), or by using wildcard patterns. See the section on directory-based tasks, for information on how the inclusion/exclusion of files works, and how to write wildcard patterns.

It is possible to use different compilers. This can be specified by either setting the global build.compiler property, which will affect all <javac> tasks throughout the build, by setting the compiler attribute, specific to the current <javac> task or by using a nested element of any typedeffed or componentdeffed type that implements org.apache.tools.ant.taskdefs.compilers.CompilerAdapter. Valid values for either the build.compiler property or the compiler attribute are:

The default is javac1.x with x depending on the JDK version you use while you are running Ant. If you wish to use a different compiler interface than those supplied, you can write a class that implements the CompilerAdapter interface (package org.apache.tools.ant.taskdefs.compilers). Supply the full classname in the build.compiler property or the compiler attribute.

The fork attribute overrides the build.compiler property or compiler attribute setting and expects a JDK 1.1 or higher to be set in JAVA_HOME.

You can also use the compiler attribute to tell Ant which JDK version it shall assume when it puts together the command line switches—even if you set fork=true. This is useful if you want to run the compiler of JDK 1.1 while your current JDK is 1.2+. If you use compiler=javac1.1 and (for example) depend=true, Ant will use the command line switch -depend instead of -Xdepend.

This task will drop all entries that point to non-existent files/directories from the classpath it passes to the compiler.

The working directory for a forked executable (if any) is the project's base directory.

Windows Note: When the modern compiler is used in unforked mode on Windows, it locks up the files present in the classpath of the <javac> task, and does not release them. The side effect of this is that you will not be able to delete or move those files later on in the build. The workaround is to fork when invoking the compiler.

If you are using Java 8 or above and your source contains native methods or fields annotated with the @Native annotation you can set the nativeheaderdir attribute in order to use the -h switch of javac to generate the native header files. Note that the logic Ant uses to determine which files to compile does not take native headers into account, i.e. if the .class is more recent than the corresponding .java file the file will not get compiled even if a native header file generated for it would be outdated.

Parameters

Attribute Description Required
srcdir Location of the java files. (See the note below.) Yes, unless nested <src> elements or modulesourcepath attribute or corresponding elements are present
destdir Location to store the class files. No
includes Comma- or space-separated list of patterns of files that must be included. No; defaults to all .java files
includesfile Name of a file. Each line of this file is taken to be an include pattern. No
excludes Comma- or space-separated list of patterns of files that must be excluded. No; defaults to default excludes or none if defaultexcludes is no
excludesfile Name of a file. Each line of this file is taken to be an exclude pattern. No
defaultexcludes Indicates whether default excludes should be used or not (yes|no). No; defaults to yes
classpath The classpath to use. No
sourcepath The sourcepath to use. To suppress the sourcepath switch, use sourcepath=. No; defaults to srcdir unless nested <src> elements are specified
bootclasspath Location of bootstrap class files. (See below for using the -X and -J-X parameters for specifying the bootstrap classpath). No
classpathref The classpath to use, given as a reference to a path defined elsewhere. No
sourcepathref The sourcepath to use, given as a reference to a path defined elsewhere. No
bootclasspathref The bootstrapclasspath to use, given as a reference to a path defined elsewhere. No
extdirs Location of installed extensions. No
encoding Encoding of source files. (Note: gcj doesn't support this option yet.) No
nowarn Indicates whether the -nowarn switch should be passed to the compiler. No; defaults to off
debug Indicates whether source should be compiled with debug information. If set to off, -g:none will be passed on the command line for compilers that support it (for other compilers, no command line argument will be used). If set to true, the value of the debuglevel attribute determines the command line argument. No; defaults to off
debuglevel Keyword list to be appended to the -g command-line switch. Legal values are none or a comma-separated list of the following keywords: lines, vars, and source. No; ignored when debug is false or any implementation other than modern, javac1.2 and jikes; by default, nothing will be appended to -g
optimize Indicates whether source should be compiled with optimization. Note that this flag is just ignored by Sun's javac since JDK 1.3 (because compile-time optimization is unnecessary). No; defaults to off
deprecation Indicates whether source should be compiled with deprecation information. No; defaults to off
verbose Asks the compiler for verbose output. No; defaults to no
depend Enables dependency tracking for compilers that support this (jikes and classic). No
includeAntRuntime Whether to include the Ant run-time libraries in the classpath. It is usually best to set this to false so the script's behavior is not sensitive to the environment in which it is run. No; defaults to yes, unless build.sysclasspath property is set
includeJavaRuntime Whether to include the default run-time libraries from the executing JVM in the classpath.
Note: In some setups the run-time libraries may be part of the "Ant run-time libraries" so you may need to explicitly set includeAntRuntime to false to ensure that the Java run-time libraries are not included.
No; defaults to no
fork Whether to execute javac using the JDK compiler externally. No; defaults to no
executable Complete path to the javac executable to use in case of fork is yes.
Since Ant 1.6 this attribute can also be used to specify the path to the executable when using jikes, jvc, gcj or sj.
No; defaults to the compiler of current JDK, ignored if fork is no
memoryInitialSize The initial size of the memory for the underlying JVM, if javac is run externally. (Examples: 83886080, 81920k, or 80m) No; defaults to the standard JVM memory setting, ignored if fork is no
memoryMaximumSize The maximum size of the memory for the underlying JVM, if javac is run externally; ignored otherwise. (Examples: 83886080, 81920k, or 80m) No; defaults to the standard JVM memory setting, ignored if fork is no
failonerror Indicates whether compilation errors will fail the build>. No; defaults to true
errorProperty The property to set to true if compilation fails. Since Ant 1.7.1. No
source Java language features accepted by compiler, as specified by the -source command-line switch. Valid feature versions are 1.3, 1.4, 1.5 or 5, etc. The attribute will be ignored by all implementations prior to javac1.4 (or modern when Ant is not running in a JVM 1.3), gcj and jikes.
If you use this attribute together with gcj or jikes, you must make sure that your version supports the -source (or -fsource for gcj) switch.
No; by default, no -source argument will be used at all unless the magic ant.build.javac.source property is set
Note that the default value depends on JDK that is running Ant. We highly recommend to always specify this attribute.
target Generate class files for specific JVM version (cross-compile). No; by default, no -target argument will be used at all unless the magic ant.build.javac.target property is set
Note that the default value depends on JDK that is running Ant and on source (see Cross-Compilation Options). We highly recommend to always specify this attribute.
compiler The compiler implementation to use. See the above list of valid compilers. No; defaults to the value of the build.compiler property, if set, or default compiler for the current JDK otherwise
listfiles Indicates whether the source files to be compiled will be listed. No; defaults to no
tempdir Where Ant should place temporary files. This is only used if the task is forked and the command line args length exceeds 4 kB. Since Ant 1.6. No; default is java.io.tmpdir
updatedProperty The property to set to true if compilation has taken place and has been successful. Since Ant 1.7.1. No
includeDestClasses This attribute controls whether to include the destination classes directory in the classpath given to the compiler. If set to true (default), previously compiled classes are on the classpath for the compiler. This means that "greedy" compilers will not recompile dependent classes that are already compiled. In general this is a good thing as it stops the compiler for doing unnecessary work. However, for some edge cases, involving generics, the javac compiler needs to compile the dependent classes to get the generics information. One example is documented in the bug report: Bug 40776 - a problem compiling a Java 5 project with generics. Setting the attribute to false will cause the compiler to recompile dependent classes. Since Ant 1.7.1. No; default is true
createMissingPackageInfoClass Some package level annotations in package-info.java files don't create any package-info.class files so Ant would recompile the same file every time.
Since Ant 1.8, an empty package-info.class is created for each package-info.java if there isn't one created by the compiler.
In some setups this additional class causes problems and it can be suppressed by setting this attribute to false. Since Ant 1.8.3.
No; default is true
modulepath Specify where to find application modules. A list of directories of modules, module files or exploded modules. since Ant 1.9.7 No
modulepathref The modulepath to use, given as reference to a path defined elsewhere. since Ant 1.9.7 No
modulesourcepath Specify where to find input source files for multiple module compilation. since Ant 1.9.7 Yes, unless srcdir attribute or nested <src> elements are present
modulesourcepathref The modulesourcepath to use, given as reference to a path defined elsewhere. since Ant 1.9.7 No
upgrademodulepath Specify the location of modules that replace upgradeable modules in the runtime image. since Ant 1.9.7 No
upgrademodulepathref The upgrademodulepath to use, given as reference to a path defined elsewhere. since Ant 1.9.7 No
nativeheaderdir Specify where to place generated native header files. Since Ant 1.9.8. No, ignored when running on JDK 7 or earlier
release Specify the value for the --release switch.
When set and running on JDK 9+ the source and target attributes as well as the bootclasspath will be ignored. Since Ant 1.9.8.
No, ignored when running on JDK 8 or earlier

Parameters specified as nested elements

This task forms an implicit FileSet and supports most attributes of <fileset> (dir becomes srcdir) as well as the nested <include>, <exclude> and <patternset> elements.

srcdir, classpath, sourcepath, bootclasspath, modulepath, modulesourcepath, upgrademodulepath and extdirs

<javac>'s srcdir, classpath, sourcepath, bootclasspath, extdirs, modulepath, modulesourcepath, and upgrademodulepath attributes are path-like structures and can also be set via nested <src> (note the different name!), <classpath>, <sourcepath>, <bootclasspath>, <extdirs>, <modulepath>, <modulesourcepath> and <upgrademodulepath> elements, respectively.

compilerarg

You can specify additional command line arguments for the compiler with nested <compilerarg> elements. These elements are specified like Command-line Arguments but have an additional attribute that can be used to enable arguments only if a given compiler implementation will be used.

Attribute Description Required
value See Command-line Arguments. Exactly one of these
line
file
path
prefix See Command-line Arguments. Since Ant 1.8. No
suffix No
compiler Only pass the specified argument if the chosen compiler implementation matches the value of this attribute. Legal values are the same as those in the above list of valid compilers.) No

compilerclasspath

Since Ant 1.8.0

A path-like structure holding the classpath to use when loading the compiler implementation if a custom class has been specified. Doesn't have any effect when using one of the built-in compilers.

Any nested element of a type that implements CompilerAdapter

Since Ant 1.8.0

If a defined type implements the CompilerAdapter interface a nested element of that type can be used as an alternative to the compiler attribute.

Examples

<javac srcdir="${src}"
       destdir="${build}"
       classpath="xyz.jar"
       debug="on"
       source="1.4"/>

compiles all .java files under the ${src} directory, and stores the .class files in the ${build} directory. The classpath used includes xyz.jar, and compiling with debug information is on. The source level is 1.4, so you can use assert statements.

<javac srcdir="${src}"
       destdir="${build}"
       fork="true"
       source="1.2"
       target="1.2"/>

compiles all .java files under the ${src} directory, and stores the .class files in the ${build} directory. This will fork off the Java compiler using the default javac executable. The source level is 1.2 (similar to 1.1 or 1.3) and the class files should be runnable under JDK 1.2+ as well.

<javac srcdir="${src}"
       destdir="${build}"
       fork="java$$javac.exe"
       source="1.5"/>

compiles all .java files under the ${src} directory, and stores the .class files in the ${build} directory. This will fork off the Java compiler, using the executable named java$javac.exe. Note that the $ sign needs to be escaped by a second one. The source level is 1.5, so you can use generics.

<javac srcdir="${src}"
       destdir="${build}"
       includes="mypackage/p1/**,mypackage/p2/**"
       excludes="mypackage/p1/testpackage/**"
       classpath="xyz.jar"
       debug="on"/>

compiles .java files under the ${src} directory, and stores the .class files in the ${build} directory. The classpath used includes xyz.jar, and debug information is on. Only files under mypackage/p1 and mypackage/p2 are used. All files in and below the mypackage/p1/testpackage directory are excluded from compilation. You didn't specify a source or target level, so the actual values used will depend on which JDK you ran Ant with.

<javac srcdir="${src}:${src2}"
       destdir="${build}"
       includes="mypackage/p1/**,mypackage/p2/**"
       excludes="mypackage/p1/testpackage/**"
       classpath="xyz.jar"
       debug="on"/>

is the same as the previous example, with the addition of a second source path, defined by the property src2. This can also be represented using nested <src> elements as follows:

<javac destdir="${build}"
       classpath="xyz.jar"
       debug="on">
  <src path="${src}"/>
  <src path="${src2}"/>
  <include name="mypackage/p1/**"/>
  <include name="mypackage/p2/**"/>
  <exclude name="mypackage/p1/testpackage/**"/>
</javac>

If you want to run the javac compiler of a different JDK, you should tell Ant, where to find the compiler and which version of JDK you will be using so it can choose the correct command line switches. The following example executes a JDK 1.1 javac in a new process and uses the correct command line switches even when Ant is running in a JVM of a different version:

<javac srcdir="${src}"
       destdir="${build}"
       fork="yes"
       executable="/opt/java/jdk1.1/bin/javac"
       compiler="javac1.1"/>

Note: If you wish to compile only source files located in certain packages below a common root, use the include/exclude attributes or <include>/<exclude> nested elements to filter for these packages. Do not include part of your package structure in the srcdir attribute (or nested <src> elements), or Ant will recompile your source files every time you run your compile target. See the Ant FAQ for additional information.

If you wish to compile only files explicitly specified and disable javac's default searching mechanism then you can unset the sourcepath attribute:

<javac sourcepath="" srcdir="${src}"
       destdir="${build}" >
  <include name="**/*.java"/>
  <exclude name="**/Example.java"/>
</javac>

That way the javac will compile all Java source files under ${src} directory but skip the examples. The compiler will even produce errors if some of the non-example files refers to them.

If you wish to compile with a special JDK (another than the one Ant is currently using), set the executable and fork attribute. Using taskname could show in the log, that these settings are fix.

<javac srcdir=""
       destdir=""
       executable="path-to-java14-home/bin/javac"
       fork="true"
       taskname="javac1.4"/>

Note: If you are using Ant on Windows and a new DOS window pops up for every use of an external compiler, this may be a problem of the JDK you are using. This problem may occur with all JDKs prior to 1.2.

If you want to activate other compiler options like lint you could use the <compilerarg> element:

<javac srcdir="${src.dir}"
       destdir="${classes.dir}"
       classpathref="libraries">
  <compilerarg value="-Xlint"/>
</javac>

If you want to use a custom CompilerAdapter org.example.MyAdapter you can either use the compiler attribute:

<javac srcdir="${src.dir}"
       destdir="${classes.dir}"
       compiler="org.example.MyAdapter"/>

or a define a type and nest this into the task like in:

<componentdef classname="org.example.MyAdapter"
              name="myadapter"/>
<javac srcdir="${src.dir}"
       destdir="${classes.dir}">
  <myadapter/>
</javac>

in which case your compiler adapter can support attributes and nested elements of its own.

<javac srcdir="${src}"
       destdir="${build}"
       includeantruntime="false"
       modulepath="modules"
       source="9"/>

compiles all .java files in a single module under the ${src} directory, and stores the .class files in the ${build} directory. The compilation uses application modules located in modules folder.The source level is 9 to enable modules.

<javac modulesourcepath="${src}/*/{gen,lin{32,64}}/classes"
       destdir="${build}"
       includeantruntime="false"
       modulepath="modules"
       source="9"/>

compiles all .java files in gen/classes, lin32/classes and lin64/classes in all source modules under the ${src} directory. Generates module directories in the ${build} directory. Each generated module directory under the ${build} directory contains .class files from corresponding source module. The * is a token representing the name of any of the modules in the compilation module set. The { ... , ... } express alternates for expansion. The compilation uses application modules located in modules folder.The source level is 9 to enable modules.

Jikes notes

You need Jikes 1.15 or later.

Jikes supports some extra options, which can be set be defining the properties shown below prior to invoking the task. The setting for each property will be in effect for all <javac> tasks throughout the build. The Ant developers are aware that this is ugly and inflexible – expect a better solution in the future. All the options are boolean, and must be set to true or yes to be interpreted as anything other than false. By default, build.compiler.warnings is true, while all others are false.

Property Description Default
build.compiler.emacs Enable emacs-compatible error messages. false
build.compiler.fulldepend Enable full dependency checking; see
the +F switch in the Jikes manual.
false
build.compiler.pedantic Enable pedantic warnings. false
build.compiler.warnings
Deprecated. Use <javac>'s nowarn attribute instead.
Don't disable warning messages. true

Jvc notes

Jvc will enable Microsoft extensions unless you set the property build.compiler.jvc.extensions to false before invoking <javac>.

Bootstrap options

The Sun javac compiler has a -bootclasspath command line option—this corresponds to the bootclasspath attribute/element of the <javac> task. The Sun compiler also allows more control over the boot classpath using the -X and -J-X attributes. One can set these by using the <compilerarg>. Since Ant 1.6.0, there is a shortcut to convert path references to strings that can by used in an OS independent fashion (see pathshortcut). For example:

<path id="lib.path.ref">
  <fileset dir="lib" includes="*.jar"/>
</path>
<javac srcdir="src" destdir="classes">
  <compilerarg arg="-Xbootclasspath/p:${toString:lib.path.ref}"/>
</javac>

OpenJDK notes

The OpenJDK project has provided the javac compiler as an open source project. The output of this project is a javac.jar which contains the javac compiler. This compiler may be used with the <javac> task with the use of a -Xbootclasspath/p Java argument. The argument needs to be given to the runtime system of the javac executable, so it needs to be prepended with a -J, for example:

<property name="patched.javac.jar"
          location="${my.patched.compiler}/dist/lib/javac.jar"/>

<presetdef name="patched.javac">
  <javac fork="yes">
    <compilerarg value="-J-Xbootclasspath/p:${patched.javac.jar}"/>
  </javac>
</presetdef>


<patched.javac srcdir="src/java" destdir="build/classes"
               debug="yes"/>

Note on package-info.java

package-info.java files were introduced in Java 5 to allow package level annotations. On compilation, if the .java file does not contain runtime annotations, there will be no corresponding .class file. Prior to Ant 1.7.1, when the <javac> task is run again, the task will try to compile the package-info.java files again.

With Ant 1.7.1, a different kind of logic was introduced that involved the timestamp of the directory that would normally contain the .class file. This logic turned out to lead to Ant not recompiling package-info.java in certain setup.

Since Ant 1.8.0, an "empty" package-info.class file is created if Ant compiles a package-info.java and no package-info.class file has been created by the compiler itself.