src/Doc/System/Scala.thy

   ensures that all provided modules are compiled and packaged (as jars). It is
   also possible to invoke @{tool scala_build} explicitly, with extra options.
 
   \<^medskip>
   The syntax of \<^path>\<open>etc/build.props\<close> follows a regular Java properties
-  file\<^footnote>\<open>\<^url>\<open>https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/util/Properties.html#load(java.io.Reader)\<close>\<close>,
+  file\<^footnote>\<open>\<^url>\<open>https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/util/Properties.html#load(java.io.Reader)\<close>\<close>,
   but the encoding is \<^verbatim>\<open>UTF-8\<close>, instead of historic \<^verbatim>\<open>ISO 8859-1\<close> from the API
   documentation.
 
   The subsequent properties are relevant for the Scala/Java build process.
   Most properties are optional: the default is an empty string (or list). File