10.15 Java bytecode compilation (deprecated)

Automake provides some minimal support for Java bytecode compilation with the JAVA primary (in addition to the support for compiling Java to native machine code; see Java Support with gcj). Note however that the interface and most features described here are deprecated. Future Automake releases will strive to provide a better and cleaner interface, which however won’t be backward-compatible; the present interface will probably be removed altogether some time after the introduction of the new interface (if that ever materializes). In any case, the current JAVA primary features are frozen and will no longer be developed, not even to take bug fixes.

Any .java files listed in a _JAVA variable will be compiled with JAVAC at build time. By default, .java files are not included in the distribution, you should use the dist_ prefix to distribute them.

Here is a typical setup for distributing .java files and installing the .class files resulting from their compilation.

javadir = $(datadir)/java
dist_java_JAVA = a.java b.java …

Currently Automake enforces the restriction that only one _JAVA primary can be used in a given Makefile.am. The reason for this restriction is that, in general, it isn’t possible to know which .class files were generated from which .java files, so it would be impossible to know which files to install where. For instance, a .java file can define multiple classes; the resulting .class file names cannot be predicted without parsing the .java file.

There are a few variables that are used when compiling Java sources:

JAVAC

The name of the Java compiler. This defaults to ‘javac’.

JAVACFLAGS

The flags to pass to the compiler. This is considered to be a user variable (see User Variables).

AM_JAVACFLAGS

More flags to pass to the Java compiler. This, and not JAVACFLAGS, should be used when it is necessary to put Java compiler flags into Makefile.am.

JAVAROOT

The value of this variable is passed to the -d option to javac. It defaults to ‘$(top_builddir)’.

CLASSPATH_ENV

This variable is a shell expression that is used to set the CLASSPATH environment variable on the javac command line. (In the future we will probably handle class path setting differently.)