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<!DOCTYPE html>
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<html lang="en">
<head>
<link rel="stylesheet" type="text/css" href="../stylesheets/style.css">
<title>Javac Task</title>
</head>
<body>
<h2 id="javac">Javac</h2>
<h3>Description</h3>
<p>Compiles a Java source tree.</p>
<p>The source and destination directory will be recursively scanned for Java source files to
compile. Only <code>.java</code> files that have no corresponding <samp>.class</samp> file or where
the <code>.class</code> file is older than the <samp>.java</samp> file will be compiled.</p>
<p><strong>Note</strong>: 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 <a href="../Tasks/depend.html"><code><depend></code></a> task for dependency checking
based on other than just existence/modification times.</p>
<p>When the source files are part of a package, the directory structure of the source tree should
follow the package hierarchy.</p>
<p>It is possible to refine the set of files that are being compiled. This can be done with
the <var>includes</var>, <var>includesfile</var>, <var>excludes</var>, and <var>excludesfile</var>
attributes. With the <var>includes</var> or <var>includesfile</var> attribute, you specify the files
you want to have included. The <var>exclude</var> or <var>excludesfile</var> 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 <var>srcdir</var> attribute or
nested <code><src></code> element(s), or by using wildcard patterns. See the section
on <a href="../dirtasks.html#directorybasedtasks">directory-based tasks</a>, for information on how
the inclusion/exclusion of files works, and how to write wildcard patterns.</p>
<p id="compilervalues">It is possible to use different compilers. This can be specified by either
setting the global <code>build.compiler</code> property, which will affect
all <code><javac></code> tasks throughout the build, by setting the <var>compiler</var>
attribute, specific to the current <code><javac></code> task or by using a nested element of
any <a href="typedef.html">typedef</a>fed or <a href="componentdef.html">componentdef</a>fed type
that implements <code>org.apache.tools.ant.taskdefs.compilers.CompilerAdapter</code>. Valid values
for either the <code>build.compiler</code> property or the <var>compiler</var> attribute are:</p>
<ul>
<li><q>classic</q> (the standard compiler of JDK 1.1/1.2) – <q>javac1.1</q>
and <q>javac1.2</q> can be used as aliases.</li>
<li><q>modern</q> (the standard compiler of JDK 1.3 and later)
– <q>javac1.3</q>, <q>javac1.4</q>, <q>javac1.5</q> and <q>javac1.6</q>, <q>javac1.7</q>
(<em>since Ant 1.8.2</em>), <q>javac1.8</q> (<em>since Ant 1.8.3</em>), <q>javac1.9</q>
(<em>since Ant 1.9.5</em>), <q>javac9</q> (<em>since Ant 1.9.8</em>) and <q>javac10+</q>
(<em>since Ant 1.10.2</em>) can be used as aliases.</li>
<li><q>jikes</q> (the <a href="http://jikes.sourceforge.net/" target="_top">Jikes</a>
compiler).</li>
<li><q>jvc</q> (the Command-Line Compiler from Microsoft's SDK for Java / Visual J++)
– <q>microsoft</q> can be used as an alias.</li>
<li><q>kjc</q>
(the <a href="https://web.archive.org/web/20050212025507/http://www.dms.at/kopi/index.html"
target="_top">kopi</a> compiler).</li>
<li><q>gcj</q> (the <code>gcj</code> compiler
from <a href="https://gcc.gnu.org/gcc-7/changes.html#java" target="_top">GCC</a>).</li>
<li><q>sj</q> (Symantec Java compiler) – <q>symantec</q> can be used as an alias.</li>
<li><q>extJavac</q> (run either modern or classic in a JVM of its own).</li>
</ul>
<p>The default is <q>javac1.x</q> with <q>x</q> 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 <code>org.apache.tools.ant.taskdefs.compilers</code>). Supply the full classname in
the <code>build.compiler</code> property or the <var>compiler</var> attribute.</p>
<p>The <var>fork</var> attribute overrides the <code>build.compiler</code> property
or <var>compiler</var> attribute setting and expects a JDK 1.1 or higher to be set
in <code>JAVA_HOME</code>.</p>
<p>You can also use the <var>compiler</var> attribute to tell Ant which JDK version it shall assume
when it puts together the command line switches—even if you set <var>fork</var>=<q>true</q>.
This is useful if you want to run the compiler of JDK 1.1 while your current JDK is 1.2+. If you
use <var>compiler</var>=<q>javac1.1</q> and (for example) <var>depend</var>=<q>true</q>, Ant will
use the command line switch <kbd>-depend</kbd> instead of <kbd>-Xdepend</kbd>.</p>
<p>This task will drop all entries that point to non-existent files/directories from the classpath
it passes to the compiler.</p>
<p>The working directory for a forked executable (if any) is the project's base directory.</p>
<p><strong>Windows Note</strong>: When the modern compiler is used in unforked mode on Windows, it
locks up the files present in the classpath of the <code><javac></code> 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.</p>
<p>If you are using Java 8 or above and your source contains native methods or fields annotated with
the <code>@Native</code> annotation you can set the <var>nativeheaderdir</var> attribute in order to
use the <kbd>-h</kbd> switch of <kbd>javac</kbd> 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 <samp>.class</samp> is more recent than the corresponding <samp>.java</samp> file the
file will not get compiled even if a native header file generated for it would be outdated.</p>
<h3>Parameters</h3>
<table class="attr">
<tr>
<th scope="col">Attribute</th>
<th scope="col">Description</th>
<th scope="col">Required</th>
</tr>
<tr>
<td>srcdir</td>
<td>Location of the java files. (See the <a href="#srcdirnote">note</a> below.)</td>
<td>Yes, unless nested <code><src></code> elements or <var>modulesourcepath</var>
attribute or corresponding elements are present</td>
</tr>
<tr>
<td>destdir</td>
<td>Location to store the class files.</td>
<td>No</td>
</tr>
<tr>
<td>includes</td>
<td>Comma- or space-separated list of patterns of files that must be included.</td>
<td>No; defaults to all <samp>.java</samp> files</td>
</tr>
<tr>
<td>includesfile</td>
<td>Name of a file. Each line of this file is taken to be an include pattern.</td>
<td>No</td>
</tr>
<tr>
<td>excludes</td>
<td>Comma- or space-separated list of patterns of files that must be excluded.</td>
<td>No; defaults to default excludes or none if <var>defaultexcludes</var> is <q>no</q></td>
</tr>
<tr>
<td>excludesfile</td>
<td>Name of a file. Each line of this file is taken to be an exclude pattern.</td>
<td>No</td>
</tr>
<tr>
<td>defaultexcludes</td>
<td>Indicates whether default excludes should be used or not (<q>yes|no</q>).</td>
<td>No; defaults to <q>yes</q></td>
</tr>
<tr>
<td>classpath</td>
<td>The classpath to use.</td>
<td>No</td>
</tr>
<tr>
<td>sourcepath</td>
<td>The sourcepath to use. To suppress the <code>sourcepath</code> switch,
use <var>sourcepath</var>=<q></q>.</td>
<td>No; defaults to <var>srcdir</var> unless nested <code><src></code> elements are
specified</td>
</tr>
<tr>
<td>bootclasspath</td>
<td>Location of bootstrap class files. (See <a href="#bootstrap">below</a> for using
the <kbd>-X</kbd> and <kbd>-J-X</kbd> parameters for specifying the bootstrap
classpath).</td>
<td>No</td>
</tr>
<tr>
<td>classpathref</td>
<td>The <var>classpath</var> to use, given as a <a href="../using.html#references">reference</a>
to a path defined elsewhere.</td>
<td>No</td>
</tr>
<tr>
<td>sourcepathref</td>
<td>The <var>sourcepath</var> to use, given as
a <a href="../using.html#references">reference</a> to a path defined elsewhere.</td>
<td>No</td>
</tr>
<tr>
<td>bootclasspathref</td>
<td>The <var>bootstrapclasspath</var> to use, given as
a <a href="../using.html#references">reference</a> to a path defined elsewhere.</td>
<td>No</td>
</tr>
<tr>
<td>extdirs</td>
<td>Location of installed extensions.</td>
<td>No</td>
</tr>
<tr>
<td>encoding</td>
<td>Encoding of source files. (<strong>Note</strong>: <code>gcj</code> doesn't support this
option yet.)</td>
<td>No</td>
</tr>
<tr>
<td>nowarn</td>
<td>Indicates whether the <kbd>-nowarn</kbd> switch should be passed to the compiler.</td>
<td>No; defaults to <q>off</q></td>
</tr>
<tr>
<td>debug</td>
<td>Indicates whether source should be compiled with debug information. If set
to <q>off</q>, <kbd>-g:none</kbd> 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 <q>true</q>, the value of the <var>debuglevel</var> attribute determines the command line
argument.</td>
<td>No; defaults to <q>off</q></td>
</tr>
<tr>
<td>debuglevel</td>
<td>Keyword list to be appended to the <kbd>-g</kbd> command-line switch. Legal values
are <q>none</q> or a comma-separated list of the following
keywords: <q>lines</q>, <q>vars</q>, and <q>source</q>.</td>
<td>No; ignored when <var>debug</var> is <q>false</q> or any implementation other
than <q>modern</q>, <q>javac1.2</q> and <q>jikes</q>; by default, nothing will be appended
to <kbd>-g</kbd></td>
</tr>
<tr>
<td>optimize</td>
<td>Indicates whether source should be compiled with optimization. <strong>Note</strong> that
this flag is just ignored by Sun's <kbd>javac</kbd> since JDK 1.3 (because compile-time
optimization is unnecessary).</td>
<td>No; defaults to <q>off</q></td>
</tr>
<tr>
<td>deprecation</td>
<td>Indicates whether source should be compiled with deprecation information.</td>
<td>No; defaults to <code>off</code></td>
</tr>
<tr>
<td>verbose</td>
<td>Asks the compiler for verbose output.</td>
<td>No; defaults to <q>no</q></td>
</tr>
<tr>
<td>depend</td>
<td>Enables dependency tracking for compilers that support this (<q>jikes</q>
and <q>classic</q>).</td>
<td>No</td>
</tr>
<tr>
<td>includeAntRuntime</td>
<td>Whether to include the Ant run-time libraries in the classpath. <em>It is usually best</em>
to set this to <q>false</q> so the script's behavior is not sensitive to the environment in
which it is run.</td>
<td>No; defaults to <q>yes</q>,
unless <a href="../sysclasspath.html"><code>build.sysclasspath</code></a> property is set</td>
</tr>
<tr>
<td>includeJavaRuntime</td>
<td>Whether to include the default run-time libraries from the executing JVM in the
classpath.<br/><strong>Note</strong>: In some setups the run-time libraries may be part of the
"Ant run-time libraries" so you may need to explicitly set <var>includeAntRuntime</var>
to <q>false</q> to ensure that the Java run-time libraries are not included.</td>
<td>No; defaults to <q>no</q></td>
</tr>
<tr>
<td>fork</td>
<td>Whether to execute <code>javac</code> using the JDK compiler externally.</td>
<td>No; defaults to <q>no</q></td>
</tr>
<tr>
<td>executable</td>
<td>Complete path to the <kbd>javac</kbd> executable to use in case of <var>fork</var>
is <q>yes</q>.<br/><em>Since Ant 1.6</em> this attribute can also be used to specify the path
to the executable when using <q>jikes</q>, <q>jvc</q>, <q>gcj</q> or <q>sj</q>.</td>
<td>No; defaults to the compiler of current JDK, ignored if <var>fork</var> is <q>no</q></td>
</tr>
<tr>
<td>memoryInitialSize</td>
<td>The initial size of the memory for the underlying JVM, if <kbd>javac</kbd> is run
externally. (Examples: <q>83886080</q>, <q>81920k</q>, or <q>80m</q>)</td>
<td>No; defaults to the standard JVM memory setting, ignored if <var>fork</var>
is <q>no</q></td>
</tr>
<tr>
<td>memoryMaximumSize</td>
<td>The maximum size of the memory for the underlying JVM, if <kbd>javac</kbd> is run
externally; ignored otherwise. (Examples: <q>83886080</q>, <q>81920k</q>, or <q>80m</q>)</td>
<td>No; defaults to the standard JVM memory setting, ignored if <var>fork</var>
is <q>no</q></td>
</tr>
<tr>
<td>failonerror</td>
<td>Indicates whether compilation errors will fail the build>.</td>
<td>No; defaults to <q>true</q></td>
</tr>
<tr>
<td>errorProperty</td>
<td>The property to set to <q>true</q> if compilation fails. <em>Since Ant 1.7.1</em>.</td>
<td>No</td>
</tr>
<tr>
<td>source</td>
<td>Java language features accepted by compiler, as specified by the <kbd>-source</kbd>
command-line switch. Valid feature versions are <q>1.3</q>, <q>1.4</q>, <q>1.5</q>
or <q>5</q>, etc. The attribute will be ignored by all implementations prior
to <q>javac1.4</q> (or <q>modern</q> when Ant is not running in a JVM 1.3), <q>gcj</q>
and <q>jikes</q>.<br/> If you use this attribute together with <q>gcj</q> or <q>jikes</q>, you
must make sure that your version supports the <kbd>-source</kbd> (or <kbd>-fsource</kbd>
for <kbd>gcj</kbd>) switch.</td>
<td>No; by default, no <kbd>-source</kbd> argument will be used at all unless the magic
<a href="../javacprops.html#source"><code>ant.build.javac.source</code></a> property is
set<br/><strong>Note that the default value depends on JDK that is running Ant. We highly
recommend to always specify this attribute.</strong></td>
</tr>
<tr>
<td>target</td>
<td>Generate class files for specific JVM version (cross-compile).</td>
<td>No; by default, no <kbd>-target</kbd> argument will be used at all unless the
magic <a href="../javacprops.html#target"><code>ant.build.javac.target</code></a> property is
set<br/><strong>Note that the default value depends on JDK that is running Ant and
on <var>source</var>
(see <a href="https://docs.oracle.com/javase/8/docs/technotes/tools/windows/javac.html#BHCJDCID"
target="_top">Cross-Compilation Options</a>). We highly recommend to always specify this
attribute.</strong></td>
</tr>
<tr>
<td>compiler</td>
<td>The compiler implementation to use. See the above <a href="#compilervalues">list</a> of
valid compilers.</td>
<td>No; defaults to the value of the <code>build.compiler</code> property, if set, or default
compiler for the current JDK otherwise</td>
</tr>
<tr>
<td>listfiles</td>
<td>Indicates whether the source files to be compiled will be listed.</td>
<td>No; defaults to <q>no</q></td>
</tr>
<tr>
<td>tempdir</td>
<td>Where Ant should place temporary files. This is only used if the task is forked and the
command line args length exceeds 4 kB. <em>Since Ant 1.6</em>.</td>
<td>No; default is <code>java.io.tmpdir</code></td>
</tr>
<tr>
<td>updatedProperty</td>
<td>The property to set to <q>true</q> if compilation has taken place and has been
successful. <em>Since Ant 1.7.1</em>.</td>
<td>No</td>
</tr>
<tr>
<td>includeDestClasses</td>
<td>This attribute controls whether to include the destination classes directory in the
classpath given to the compiler. If set to <q>true</q> (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 <kbd>javac</kbd> compiler needs to compile the dependent classes to get the generics
information. One example is documented in the bug
report: <a href="https://issues.apache.org/bugzilla/show_bug.cgi?id=40776" target="_top">Bug
40776 - a problem compiling a Java 5 project with generics</a>. Setting the attribute
to <q>false</q> will cause the compiler to recompile dependent classes. <em>Since Ant
1.7.1</em>.</td>
<td>No; default is <q>true</q></td>
</tr>
<tr>
<td>createMissingPackageInfoClass</td>
<td>Some package level annotations in <samp>package-info.java</samp> files don't create
any <samp>package-info.class</samp> files so Ant would recompile the same file every
time.<br/><em>Since Ant 1.8</em>, an empty <samp>package-info.class</samp> is created for
each <samp>package-info.java</samp> if there isn't one created by the compiler.<br/>In some
setups this additional class causes problems and it can be suppressed by setting this
attribute to <q>false</q>. <em>Since Ant 1.8.3</em>.</td>
<td>No; default is <q>true</q></td>
</tr>
<tr>
<td>modulepath</td>
<td>Specify where to find application modules. A list of directories of modules, module files or
exploded modules. <em>since Ant 1.9.7</em></td>
<td>No</td>
</tr>
<tr>
<td>modulepathref</td>
<td>The <var>modulepath</var> to use, given as <a href="../using.html#references">reference</a>
to a path defined elsewhere. <em>since Ant 1.9.7</em></td>
<td>No</td>
</tr>
<tr>
<td>modulesourcepath</td>
<td>Specify where to find input source files for multiple module compilation. <em>since Ant
1.9.7</em></td>
<td>Yes, unless <var>srcdir</var> attribute or nested <code><src></code> elements are
present</td>
</tr>
<tr>
<td>modulesourcepathref</td>
<td>The <var>modulesourcepath</var> to use, given
as <a href="../using.html#references">reference</a> to a path defined elsewhere. <em>since
Ant 1.9.7</em></td>
<td>No</td>
</tr>
<tr>
<td>upgrademodulepath</td>
<td>Specify the location of modules that replace upgradeable modules in the runtime
image. <em>since Ant 1.9.7</em></td>
<td>No</td>
</tr>
<tr>
<td>upgrademodulepathref</td>
<td>The <var>upgrademodulepath</var> to use, given
as <a href="../using.html#references">reference</a> to a path defined elsewhere. <em>since Ant
1.9.7</em></td>
<td>No</td>
</tr>
<tr>
<td>nativeheaderdir</td>
<td>Specify where to place generated native header files. <em>Since Ant 1.9.8</em>.
<td>No, ignored when running on JDK 7 or earlier</td>
</tr>
<tr>
<td>release</td>
<td>Specify the value for the <kbd>--release</kbd> switch.<br/>When set and running on JDK 9+
the <var>source</var> and <var>target</var> attributes as well as the <var>bootclasspath</var>
will be ignored. <em>Since Ant 1.9.8</em>.
<td>No, ignored when running on JDK 8 or earlier</td>
</tr>
</table>
<h3>Parameters specified as nested elements</h3>
<p>This task forms an implicit <a href="../Types/fileset.html">FileSet</a> and supports most
attributes of <code><fileset></code> (<var>dir</var> becomes <var>srcdir</var>) as well as the
nested <code><include></code>, <code><exclude></code>
and <code><patternset></code> elements.</p>
<h4><code>srcdir</code>, <code>classpath</code>, <code>sourcepath</code>, <code>bootclasspath</code>,
<code>modulepath</code>, <code>modulesourcepath</code>, <code>upgrademodulepath</code> and <code>extdirs</code></h4>
<p><code><javac></code>'s <var>srcdir</var>, <var>classpath</var>, <var>sourcepath</var>,
<var>bootclasspath</var>, <var>extdirs</var>, <var>modulepath</var>, <var>modulesourcepath</var>,
and <var>upgrademodulepath</var> attributes are <a href="../using.html#path">path-like
structures</a> and can also be set via nested <code><src></code> (note the different
name!), <code><classpath></code>, <code><sourcepath></code>, <code><bootclasspath></code>,
<code><extdirs></code>, <code><modulepath></code>, <code><modulesourcepath></code>
and <code><upgrademodulepath></code> elements, respectively.</p>
<h4>compilerarg</h4>
<p>You can specify additional command line arguments for the compiler with
nested <code><compilerarg></code> elements. These elements are specified
like <a href="../using.html#arg">Command-line Arguments</a> but have an additional attribute that
can be used to enable arguments only if a given compiler implementation will be used.</p>
<table class="attr">
<tr>
<th scope="col">Attribute</th>
<th scope="col">Description</th>
<th scope="col">Required</th>
</tr>
<tr>
<td>value</td>
<td rowspan="4">See <a href="../using.html#arg">Command-line Arguments</a>.</td>
<td rowspan="4">Exactly one of these</td>
</tr>
<tr>
<td class="var">line</td>
</tr>
<tr>
<td class="var">file</td>
</tr>
<tr>
<td class="var">path</td>
</tr>
<tr>
<td>prefix</td>
<td rowspan="2">See <a href="../using.html#arg">Command-line Arguments</a>. <em>Since Ant
1.8</em>.</td>
<td>No</td>
</tr>
<tr>
<td>suffix</td>
<td>No</td>
</tr>
<tr>
<td>compiler</td>
<td>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 <a href="#compilervalues">list</a> of valid compilers.)</td>
<td>No</td>
</tr>
</table>
<h4>compilerclasspath</h4>
<p><em>Since Ant 1.8.0</em></p>
<p>A <a href="../using.html#path">path-like structure</a> 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.</p>
<h4>Any nested element of a type that implements <code>CompilerAdapter</code></h4>
<p><em>Since Ant 1.8.0</em></p>
<p>If a defined type implements the <code>CompilerAdapter</code> interface a nested element of that
type can be used as an alternative to the <var>compiler</var> attribute.</p>
<h3>Examples</h3>
<p>Compile all <samp>.java</samp> files under the <samp>${src}</samp> directory, and store
the <samp>.class</samp> files in the <samp>${build}</samp> directory. The classpath used
includes <samp>xyz.jar</samp>, and compiling with debug information is on. The source level
is <q>1.4</q>, so you can use <code>assert</code> statements.</p>
<pre>
<javac srcdir="${src}"
destdir="${build}"
classpath="xyz.jar"
debug="on"
source="1.4"/></pre>
<p>Compile all <samp>.java</samp> files under the <samp>${src}</samp> directory, and store
the <samp>.class</samp> files in the <samp>${build}</samp> directory. Java compiler is forked using
the default <kbd>javac</kbd> executable. The source level is <q>1.2</q> (similar to <q>1.1</q>
or <q>1.3</q>) and the class files should be runnable under JDK 1.2+ as well.</p>
<pre>
<javac srcdir="${src}"
destdir="${build}"
fork="true"
source="1.2"
target="1.2"/></pre>
<p>Compile all <samp>.java</samp> files under the <samp>${src}</samp> directory, and store
the <samp>.class</samp> files in the <samp>${build}</samp> directory. Java compiler is forked using
the executable named <kbd>java$javac.exe</kbd>. Note that the <q>$</q> sign needs to be escaped by a
second one. The source level is <q>1.5</q>, so you can use generics.</p>
<pre>
<javac srcdir="${src}"
destdir="${build}"
fork="java$$javac.exe"
source="1.5"/></pre>
<p>Compile <samp>.java</samp> files under the <samp>${src}</samp> directory, and store
the <samp>.class</samp> files in the <code>${build}</code> directory. The classpath used
includes <samp>xyz.jar</samp>, and debug information is on. Only files
under <samp>mypackage/p1</samp> and <samp>mypackage/p2</samp> are used. All files in and below
the <samp>mypackage/p1/testpackage</samp> 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.</p>
<pre>
<javac srcdir="${src}"
destdir="${build}"
includes="mypackage/p1/**,mypackage/p2/**"
excludes="mypackage/p1/testpackage/**"
classpath="xyz.jar"
debug="on"/></pre>
<p>This is the same as the previous example, with the addition of a second source path, defined by
the property <samp>src2</samp>. This can also be represented using nested <code><src></code>
elements as follows:</p>
<pre>
<javac destdir="${build}"
classpath="xyz.jar"
debug="on">
<src path="${src}"/>
<src path="${src2}"/>
<include name="mypackage/p1/**"/>
<include name="mypackage/p2/**"/>
<exclude name="mypackage/p1/testpackage/**"/>
</javac></pre>
<p>If you want to run the <kbd>javac</kbd> compiler of a different JDK, you should tell Ant where to
find the compiler and which version of JDK you will be using so it can choose the correct command
line switches. The following example executes a JDK 1.1 <kbd>javac</kbd> in a new process and uses
the correct command line switches even when Ant is running in a JVM of a different version:</p>
<pre>
<javac srcdir="${src}"
destdir="${build}"
fork="yes"
executable="/opt/java/jdk1.1/bin/javac"
compiler="javac1.1"/></pre>
<p id="srcdirnote"><strong>Note</strong>: If you wish to compile only source files located in
certain packages below a common root, use the <var>include</var>/<var>exclude</var> attributes
or <code><include></code>/<code><exclude></code> nested elements to filter for these
packages. Do not include part of your package structure in the <var>srcdir</var> attribute (or
nested <code><src></code> elements), or Ant will recompile your source files every time you
run your compile target. See the <a href="https://ant.apache.org/faq.html#always-recompiles"
target="_top">Ant FAQ</a> for additional information.</p>
<p>If you wish to compile only files explicitly specified and disable <code>javac</code>'s default
searching mechanism then you can unset the <var>sourcepath</var> attribute:</p>
<pre>
<javac sourcepath="" srcdir="${src}"
destdir="${build}" >
<include name="**/*.java"/>
<exclude name="**/Example.java"/>
</javac></pre>
<p>That way the <code>javac</code> will compile all Java source files under <samp>${src}</samp>
directory but skip the examples. The compiler will even produce errors if some of the non-example
files refers to them.</p>
<p>If you wish to compile with a special JDK (another than the one Ant is currently using), set
the <var>executable</var> and <var>fork</var> attribute. Using <var>taskname</var> could show in the
log, that these settings are fix.</p>
<pre>
<javac srcdir=""
destdir=""
executable="path-to-java14-home/bin/javac"
fork="true"
taskname="javac1.4"/></pre>
<p><strong>Note</strong>: 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.</p>
<p>If you want to activate other compiler options like <code>lint</code> you could use
the <code><compilerarg></code> element:</p>
<pre>
<javac srcdir="${src.dir}"
destdir="${classes.dir}"
classpathref="libraries">
<compilerarg value="-Xlint"/>
</javac></pre>
<p>If you want to use a custom CompilerAdapter <code>org.example.MyAdapter</code> you can either use
the <var>compiler</var> attribute:</p>
<pre>
<javac srcdir="${src.dir}"
destdir="${classes.dir}"
compiler="org.example.MyAdapter"/></pre>
<p>or a define a type and nest this into the task like in:</p>
<pre>
<componentdef classname="org.example.MyAdapter"
name="myadapter"/>
<javac srcdir="${src.dir}"
destdir="${classes.dir}">
<myadapter/>
</javac></pre>
<p>in which case your compiler adapter can support attributes and nested elements of its own.</p>
<p>The following examples demonstrate the use of Java 9+ modules.</p>
<p>Compile all <samp>.java</samp> files in a single module under the <samp>${src}</samp> directory,
and store the <samp>.class</samp> files in the <code>${build}</code> directory. The compilation uses
application modules located in <samp>modules</samp> folder. The source level is <q>9</q> to enable
modules.</p>
<pre>
<javac srcdir="${src}"
destdir="${build}"
includeantruntime="false"
modulepath="modules"
source="9"/></pre>
<p>Compile all <samp>.java</samp> files in <samp>gen/classes</samp>, <samp>lin32/classes</samp>
and <code>lin64/classes</code> in all source modules under the <code>${src}</code>
directory. Generate module directories in the <samp>${build}</samp> directory. Each generated module
directory under the <samp>${build}</samp> directory contains <code>.class</code> files from
corresponding source module. The <samp>*</samp> is a token representing the name of any of the
modules in the compilation module set. The <code>{ ... , ... }</code> express alternates for
expansion. The compilation uses application modules located in <code>modules</code> folder. The
source level is <q>9</q> to enable modules.</p>
<pre>
<javac modulesourcepath="${src}/*/{gen,lin{32,64}}/classes"
destdir="${build}"
includeantruntime="false"
modulepath="modules"
source="9"/></pre>
<h3 id="jikes">Jikes notes</h3>
<p>You need Jikes 1.15 or later.</p>
<p>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 <code><javac></code> 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 <q>true</q> or <q>yes</q> to be interpreted as anything other
than <q>false</q>. By default, <code>build.compiler.warnings</code> is <q>true</q>, while all others
are <q>false</q>.</p>
<table>
<tr>
<th scope="col">Property</th>
<th scope="col">Description</th>
<th scope="col">Default</th>
</tr>
<tr>
<td><code>build.compiler.emacs</code></td>
<td>Enable emacs-compatible error messages.</td>
<td><q>false</q></td>
</tr>
<tr>
<td><code>build.compiler.fulldepend</code></td>
<td>Enable full dependency checking; see<br/> the <code>+F</code> switch in the Jikes
manual.</td>
<td><q>false</q></td>
</tr>
<tr>
<td><code>build.compiler.pedantic</code></td>
<td>Enable pedantic warnings.</td>
<td><q>false</q></td>
</tr>
<tr>
<td><code>build.compiler.warnings</code><br/><em><u>Deprecated</u></em>.
Use <code><javac></code>'s <var>nowarn</var> attribute instead.</td>
<td>Don't disable warning messages.</td>
<td><q>true</q></td>
</tr>
</table>
<h3 id="jvc">Jvc notes</h3>
<p><q>Jvc</q> will enable Microsoft extensions unless you set the
property <code>build.compiler.jvc.extensions</code> to <q>false</q> before
invoking <code><javac></code>.</p>
<h3 id="bootstrap">Bootstrap options</h3>
<p>The Sun <kbd>javac</kbd> compiler has a <kbd>-bootclasspath</kbd> command line
option—this corresponds to the <var>bootclasspath</var> attribute/element of
the <code><javac></code> task. The Sun compiler also allows more control over the boot
classpath using the <kbd>-X</kbd> and <kbd>-J-X</kbd> attributes. One can set these by using
the <code><compilerarg></code>. <em>Since Ant 1.6.0</em>, there is a shortcut to convert path
references to strings that can by used in an OS independent fashion
(see <a href="../using.html#pathshortcut">pathshortcut</a>). For example:</p>
<pre>
<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></pre>
<h3>OpenJDK notes</h3>
<p>The <a href="https://openjdk.java.net/" target="_top">OpenJDK</a> project has provided
the <code>javac</code> <a href="https://openjdk.java.net/groups/compiler/" target="_top">compiler</a>
as an open source project. The output of this project is a <code>javac.jar</code> which contains
the <kbd>javac</kbd> compiler. This compiler may be used with the <code><javac></code> task
with the use of a <kbd>-Xbootclasspath/p</kbd> Java argument. The argument needs to be given to the
runtime system of the <kbd>javac</kbd> executable, so it needs to be prepended with a <kbd>-J</kbd>,
for example:</p>
<pre>
<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"/></pre>
<h3>Note on package-info.java</h3>
<p><samp>package-info.java</samp> files were introduced in Java 5 to allow package level
annotations. On compilation, if the <code>.java</code> file does not contain runtime annotations,
there will be no corresponding <code>.class</code> file. Prior to Ant 1.7.1, when
the <code><javac></code> task is run again, the task will try to compile
the <samp>package-info.java</samp> files again.</p>
<p>With Ant 1.7.1, a different kind of logic was introduced that involved the timestamp of the
directory that would normally contain the <samp>.class</samp> file. This logic turned out to lead
to Ant not recompiling <samp>package-info.java</samp> in certain setup.</p>
<p><em>Since Ant 1.8.0</em>, an "empty" <samp>package-info.class</samp> file is created if Ant
compiles a <samp>package-info.java</samp> and no <samp>package-info.class</samp> file has been
created by the compiler itself.</p>
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