Javac Task

## 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 different 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:

- `classic` (the standard compiler of JDK 1.1/1.2) – `javac1.1` and `javac1.2` can be used as aliases.
- `modern` (the standard compiler of JDK 1.3 and later) – `javac1.3` and `javac1.4` and `javac1.5` and `javac1.6` and `javac1.7` (since Ant 1.8.2) and `javac1.8` (since Ant 1.8.3) and
`javac1.9` (since Ant 1.9.5) can be used as aliases.
- `jikes` (the Jikes compiler).
- `jvc` (the Command-Line Compiler from Microsoft's SDK for Java / Visual J++) – `microsoft` can be used as an alias.
- `kjc` (the kopi compiler).
- `gcj` (the gcj compiler from gcc).
- `sj` (Symantec java compiler) – `symantec` can be used as an alias.
- `extJavac` (run either modern or classic in a JVM of its own).

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 JDK1.1 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 you 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.

### Parameters

Attribute | Description | Required
srcdir | Location of the java files. (See the note below.) | Yes, unless nested `<src>` elements or `modulesourcepath` attribute or elements are present.
destdir | Location to store the class files. | No
includes | Comma- or space-separated list of files (may be specified using wildcard patterns) that must be included; all `.java` files are included when omitted. | No
includesfile | The name of a file that contains a list of files to include (may be specified using wildcard patterns). | No
excludes | Comma- or space-separated list of files (may be specified using wildcard patterns) that must be excluded; no files (except default excludes) are excluded when omitted. | No
excludesfile | The name of a file that contains a list of files to exclude (may be specified using wildcard patterns). | No
classpath | The classpath to use. | No
sourcepath | The sourcepath to use; defaults to the value of the srcdir attribute (or nested `<src>` elements). To suppress the sourcepath switch, use `sourcepath=""`. | No
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 | Location of bootstrap class files, 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; defaults to `off`. | No
debug | Indicates whether source should be compiled with debug information; defaults to `off`. 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
debuglevel | Keyword list to be appended to the `-g` command-line switch. This will be ignored by all implementations except `modern`, `classic(ver >= 1.2)` and `jikes`. Legal values are `none` or a comma-separated list of the following keywords: `lines`, `vars`, and `source`. If `debuglevel` is not specified, by default, nothing will be appended to `-g`. If `debug` is not turned on, this attribute will be ignored. | No
optimize | Indicates whether source should be compiled with optimization; defaults to `off`. Note that this flag is just ignored by Sun's `javac` starting with JDK 1.3 (since compile-time optimization is unnecessary). | No
deprecation | Indicates whether source should be compiled with deprecation information; defaults to `off`. | No
target | Generate class files for specific VM version (e.g., `1.1` or `1.2`). Note that the default value depends on the JVM that is running Ant. In particular, if you use JDK 1.4+ the generated classes will not be usable for a 1.1 Java VM unless you explicitly set this attribute to the value 1.1 (which is the default value for JDK 1.1 to 1.3). We highly recommend to always specify this attribute. A default value for this attribute can be provided using the magic `ant.build.javac.target` property. | No
verbose | Asks the compiler for verbose output; defaults to `no`. | 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; defaults to `yes`, unless `build.sysclasspath` is set. 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
includeJavaRuntime | Whether to include the default run-time libraries from the executing VM in the classpath; defaults to `no`. 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
fork | Whether to execute `javac` using the JDK compiler externally; defaults to `no`. | No
executable | Complete path to the `javac` executable to use in case of `fork="yes"`. Defaults to the compiler of the Java version that is currently running Ant. Ignored if `fork="no"`. 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
memoryInitialSize | The initial size of the memory for the underlying VM, if `javac` is run externally; ignored otherwise. Defaults to the standard VM memory setting. (Examples: `83886080`, `81920k`, or `80m`) | No
memoryMaximumSize | The maximum size of the memory for the underlying VM, if `javac` is run externally; ignored otherwise. Defaults to the standard VM memory setting. (Examples: `83886080`, `81920k`, or `80m`) | No
failonerror | Indicates whether compilation errors will fail the build; defaults to `true`. | No
errorProperty | The property to set (to the value "true") if compilation fails. Since Ant 1.7.1. | No
source | Value of the `-source` command-line switch; will be ignored by all implementations prior to `javac1.4` (or `modern` when Ant is not running in a 1.3 VM), `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. By default, no `-source` argument will be used at all. Note that the default value depends on the JVM that is running Ant. We highly recommend to always specify this attribute. A default value for this attribute can be provided using the magic `ant.build.javac.source` property. | No
compiler | The compiler implementation to use. If this attribute is not set, the value of the `build.compiler` property, if set, will be used. Otherwise, the default compiler for the current VM will be used. (See the above list of valid compilers.) | No
listfiles | Indicates whether the source files to be compiled will be listed; defaults to `no`. | No
tempdir | Where Ant should place temporary files. This is only used if the task is forked and the command line args length exceeds 4k. Since Ant 1.6. | No; default is java.io.tmpdir.
updatedProperty | The property to set (to the value "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. The default value of this is "true" and this means that 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. Starting with Ant 1.8 Ant will create an empty `package-info.class` 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

### 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 javac 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 javac 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 Java VM 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 < 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 affect 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 opensource 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 Java5 to allow package level annotations. On compilation, if the java file does not contain runtime annotations, there will be no .class file for the java file. Up 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.

Starting with Ant 1.8.0 Ant will create "empty" `package-info.class` files if it compiles a `package-info.java` and no `package-info.class` file has been created by the compiler itself.