26.2. How SCons Handles Java Dependencies

In addition to searching the source directory for .java files, SCons actually runs the .java files through a stripped-down Java parser that figures out what classes are defined. In other words, SCons knows, without you having to tell it, what .class files will be produced by the javac call. So our one-liner example from the preceding section:

      Java('classes', 'src')
    

Will not only tell you reliably that the .class files in the classes subdirectory are up-to-date:

      % scons -Q
      javac -d classes -sourcepath src src/Example1.java src/Example2.java src/Example3.java
      % scons -Q classes
      scons: `classes' is up to date.
    

But it will also remove all of the generated .class files, even for inner classes, without you having to specify them manually. For example, if our Example1.java and Example3.java files both define additional classes, and the class defined in Example2.java has an inner class, running scons -c will clean up all of those .class files as well:

      % scons -Q
      javac -d classes -sourcepath src src/Example1.java src/Example2.java src/Example3.java
      % scons -Q -c classes
      Removed classes/Example1.class
      Removed classes/AdditionalClass1.class
      Removed classes/Example2$Inner2.class
      Removed classes/Example2.class
      Removed classes/Example3.class
      Removed classes/AdditionalClass3.class
    

To ensure correct handling of .class dependencies in all cases, you need to tell SCons which Java version is being used. This is needed because Java 1.5 changed the .class file names for nested anonymous inner classes. Use the JAVAVERSION construction variable to specify the version in use. With Java 1.6, the one-liner example can then be defined like this:

      Java('classes', 'src', JAVAVERSION='1.6')
    

See JAVAVERSION in the man page for more information.