java: add an example

* examples/java/Calc.y: New, based on test 495: "Calculator
parse.error=verbose %locations".
* examples/java/Calc.test, examples/java/local.mk: New.

* configure.ac (ENABLE_JAVA): New.
* examples/test (prog): Be ready to run Java programs.

examples/java/local.mk

@@ -0,0 +1,34 @@
+## Copyright (C) 2018 Free Software Foundation, Inc.
+##
+## This program is free software: you can redistribute it and/or modify
+## it under the terms of the GNU General Public License as published by
+## the Free Software Foundation, either version 3 of the License, or
+## (at your option) any later version.
+##
+## This program is distributed in the hope that it will be useful,
+## but WITHOUT ANY WARRANTY; without even the implied warranty of
+## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+## GNU General Public License for more details.
+##
+## You should have received a copy of the GNU General Public License
+## along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+javadir = $(docdir)/%D%
+
+## ------ ##
+## Calc.  ##
+## ------ ##
+
+if ENABLE_JAVA
+  check_SCRIPTS += %D%/Calc.class
+  TESTS += %D%/Calc.test
+endif
+
+%D%/Calc.java: %D%/Calc.y $(BISON_IN) $(dist_pkgdata_DATA)
+	$(AM_V_GEN)$(BISON) $< -o $@
+
+%D%/Calc.class: %D%/Calc.java
+	$(AM_V_GEN) $(SHELL) $(top_builddir)/javacomp.sh $<
+
+dist_java_DATA = %D%/Calc.y
+CLEANFILES += %D%/Calc.class %D%/Calc.java