diff --git a/Checkstyle.xml b/Checkstyle.xml
index 6788535..36dbd1f 100644
--- a/Checkstyle.xml
+++ b/Checkstyle.xml
@@ -4,7 +4,7 @@
     "https://checkstyle.org/dtds/configuration_1_3.dtd">
 
 <!--
-Checkstyle configuration for Think Java, 2nd Edition.
+Checkstyle 8.44 configuration for Think Java, 2nd Edition.
 -->
 <module name="Checker">
     <property name="severity" value="warning"/>
@@ -82,6 +82,7 @@ Checkstyle configuration for Think Java, 2nd Edition.
             <property name="scope" value="private"/>
         </module>
         <module name="NonEmptyAtclauseDescription"/>
+        <module name="RequireEmptyLineBeforeBlockTagGroup"/>
         <module name="SummaryJavadocCheck"/>
 
         <!-- See https://checkstyle.sourceforge.io/config_misc.html -->
diff --git a/Formatter.xml b/Formatter.xml
index a16cdb8..ab6e68e 100644
--- a/Formatter.xml
+++ b/Formatter.xml
@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="UTF-8" standalone="no"?>
-<profiles version="20">
-    <profile kind="CodeFormatterProfile" name="Think Java, 2nd Edition" version="20">
+<profiles version="21">
+    <profile kind="CodeFormatterProfile" name="Think Java, 2nd Edition" version="21">
         <setting id="org.eclipse.jdt.core.formatter.insert_space_after_ellipsis" value="insert"/>
         <setting id="org.eclipse.jdt.core.formatter.insert_space_after_comma_in_enum_declarations" value="insert"/>
         <setting id="org.eclipse.jdt.core.formatter.insert_space_before_comma_in_allocation_expression" value="do not insert"/>