refer to THIS_JAVA dynamically, and treat ISABELLE_JAVA as static default -- relevant for nested JVM invocation within an existing Isabelle enviroment;
#!/usr/bin/env bash
#
# Author: Makarius
#
# DESCRIPTION: invoke Java within the Isabelle environment
CLASSPATH="$(jvmpath "$CLASSPATH")"
exec "${THIS_JAVA:-ISABELLE_JAVA}" "$@"