============
Java Sources
============

sbt has support for compiling Java sources with the limitation that
dependency tracking is limited to the dependencies present in compiled
class files.

Usage
=====

-  ``compile`` will compile the sources under ``src/main/java`` by
   default.
-  ``test-compile`` will compile the sources under ``src/test/java`` by
   default.

Pass options to the Java compiler by setting ``javac-options``:

::

    javacOptions += "-g:none"

As with options for the Scala compiler, the arguments are not parsed by
sbt. Multi-element options, such as ``-source 1.5``, are specified like:

::

    javacOptions ++= Seq("-source", "1.5")

You can specify the order in which Scala and Java sources are built with
the ``compile-order`` setting. Possible values are from the
``CompileOrder`` enumeration: ``Mixed``, ``JavaThenScala``, and
``ScalaThenJava``. If you have circular dependencies between Scala and
Java sources, you need the default, ``Mixed``, which passes both Java
and Scala sources to ``scalac`` and then compiles the Java sources with
``javac``. If you do not have circular dependencies, you can use one of
the other two options to speed up your build by not passing the Java
sources to ``scalac``. For example, if your Scala sources depend on your
Java sources, but your Java sources do not depend on your Scala sources,
you can do:

::

    compileOrder := CompileOrder.JavaThenScala

To specify different orders for main and test sources, scope the setting
by configuration:

::

    // Java then Scala for main sources
    compileOrder in Compile := CompileOrder.JavaThenScala

    // allow circular dependencies for test sources
    compileOrder in Test := CompileOrder.Mixed

Note that in an incremental compilation setting, it is not practical to
ensure complete isolation between Java sources and Scala sources because
they share the same output directory. So, previously compiled classes
not involved in the current recompilation may be picked up. A clean
compile will always provide full checking, however.

By default, sbt includes ``src/main/scala`` and ``src/main/java`` in its
list of unmanaged source directories. For Java-only projects, the
unnecessary Scala directories can be ignored by modifying
``unmanagedSourceDirectories``:

::

    // Include only src/main/java in the compile configuration
    unmanagedSourceDirectories in Compile <<= Seq(javaSource in Compile).join

    // Include only src/test/java in the test configuration
    unmanagedSourceDirectories in Test <<= Seq(javaSource in Test).join

However, there should not be any harm in leaving the Scala directories
if they are empty.