diff --git a/config/checkstyle/checkstyle.xml b/config/checkstyle/checkstyle.xml
index bed9ee2..af17869 100644
--- a/config/checkstyle/checkstyle.xml
+++ b/config/checkstyle/checkstyle.xml
@@ -1,26 +1,26 @@
 <?xml version="1.0"?>
 <!DOCTYPE module PUBLIC
-          "-//Puppy Crawl//DTD Check Configuration 1.3//EN"
-          "http://www.puppycrawl.com/dtds/configuration_1_3.dtd">
+          "-//Checkstyle//DTD Checkstyle Configuration 1.3//EN"
+          "https://checkstyle.org/dtds/configuration_1_3.dtd">
 
 <!--
 
   Checkstyle configuration that checks the sun coding conventions from:
 
     - the Java Language Specification at
-      http://java.sun.com/docs/books/jls/second_edition/html/index.html
+      https://docs.oracle.com/javase/specs/jls/se11/html/index.html
 
-    - the Sun Code Conventions at http://java.sun.com/docs/codeconv/
+    - the Sun Code Conventions at https://www.oracle.com/technetwork/java/codeconvtoc-136057.html
 
     - the Javadoc guidelines at
-      http://java.sun.com/j2se/javadoc/writingdoccomments/index.html
+      https://www.oracle.com/technetwork/java/javase/documentation/index-137868.html
 
-    - the JDK Api documentation http://java.sun.com/j2se/docs/api/index.html
+    - the JDK Api documentation https://docs.oracle.com/en/java/javase/11/
 
     - some best practices
 
   Checkstyle is very configurable. Be sure to read the documentation at
-  http://checkstyle.sf.net (or in your downloaded distribution).
+  https://checkstyle.org (or in your downloaded distribution).
 
   Most Checks are configurable, be sure to consult the documentation.
 
@@ -34,35 +34,41 @@
     <!--
         If you set the basedir property below, then all reported file
         names will be relative to the specified directory. See
-        http://checkstyle.sourceforge.net/5.x/config.html#Checker
+        https://checkstyle.org/5.x/config.html#Checker
 
         <property name="basedir" value="${basedir}"/>
     -->
 
     <property name="fileExtensions" value="java, properties, xml"/>
 
+    <!-- Excludes all 'module-info.java' files              -->
+    <!-- See https://checkstyle.org/config_filefilters.html -->
+    <module name="BeforeExecutionExclusionFileFilter">
+        <property name="fileNamePattern" value="module\-info\.java$"/>
+    </module>
+
     <!-- Checks that a package-info.java file exists for each package.     -->
-    <!-- See http://checkstyle.sf.net/config_javadoc.html#JavadocPackage -->
+    <!-- See https://checkstyle.org/config_javadoc.html#JavadocPackage -->
     <module name="JavadocPackage"/>
 
     <!-- Checks whether files end with a new line.                        -->
-    <!-- See http://checkstyle.sf.net/config_misc.html#NewlineAtEndOfFile -->
+    <!-- See https://checkstyle.org/config_misc.html#NewlineAtEndOfFile -->
     <module name="NewlineAtEndOfFile"/>
 
     <!-- Checks that property files contain the same keys.         -->
-    <!-- See http://checkstyle.sf.net/config_misc.html#Translation -->
+    <!-- See https://checkstyle.org/config_misc.html#Translation -->
     <module name="Translation"/>
 
     <!-- Checks for Size Violations.                    -->
-    <!-- See http://checkstyle.sf.net/config_sizes.html -->
+    <!-- See https://checkstyle.org/config_sizes.html -->
     <module name="FileLength"/>
 
     <!-- Checks for whitespace                               -->
-    <!-- See http://checkstyle.sf.net/config_whitespace.html -->
+    <!-- See https://checkstyle.org/config_whitespace.html -->
     <module name="FileTabCharacter"/>
 
     <!-- Miscellaneous other checks.                   -->
-    <!-- See http://checkstyle.sf.net/config_misc.html -->
+    <!-- See https://checkstyle.org/config_misc.html -->
     <module name="RegexpSingleline">
        <property name="format" value="\s+$"/>
        <property name="minimum" value="0"/>
@@ -71,7 +77,7 @@
     </module>
 
     <!-- Checks for Headers                                -->
-    <!-- See http://checkstyle.sf.net/config_header.html   -->
+    <!-- See https://checkstyle.org/config_header.html   -->
     <!-- <module name="Header"> -->
     <!--   <property name="headerFile" value="${checkstyle.header.file}"/> -->
     <!--   <property name="fileExtensions" value="java"/> -->
@@ -80,20 +86,18 @@
     <module name="TreeWalker">
 
         <!-- Checks for Javadoc comments.                     -->
-        <!-- See http://checkstyle.sf.net/config_javadoc.html -->
-        <module name="JavadocMethod">
-            <property name="excludeScope" value="private"/>
-        </module>
-        <module name="JavadocType">
-            <property name="excludeScope" value="private"/>
-        </module>
+        <!-- See https://checkstyle.org/config_javadoc.html -->
+        <module name="InvalidJavadocPosition"/>
+        <module name="JavadocMethod"/>
+        <module name="JavadocType"/>
         <module name="JavadocVariable">
             <property name="excludeScope" value="private"/>
         </module>
         <module name="JavadocStyle"/>
+        <module name="MissingJavadocMethod"/>
 
         <!-- Checks for Naming Conventions.                  -->
-        <!-- See http://checkstyle.sf.net/config_naming.html -->
+        <!-- See https://checkstyle.org/config_naming.html -->
         <module name="ConstantName"/>
         <module name="LocalFinalVariableName"/>
         <module name="LocalVariableName"/>
@@ -105,7 +109,7 @@
         <module name="TypeName"/>
 
         <!-- Checks for imports                              -->
-        <!-- See http://checkstyle.sf.net/config_import.html -->
+        <!-- See https://checkstyle.org/config_import.html -->
         <module name="AvoidStarImport"/>
         <module name="IllegalImport"/> <!-- defaults to sun.* packages -->
         <module name="RedundantImport"/>
@@ -114,7 +118,7 @@
         </module>
 
         <!-- Checks for Size Violations.                    -->
-        <!-- See http://checkstyle.sf.net/config_sizes.html -->
+        <!-- See https://checkstyle.org/config_sizes.html -->
         <module name="LineLength">
             <property name="max" value="120"/>
         </module>
@@ -122,7 +126,7 @@
         <module name="ParameterNumber"/>
 
         <!-- Checks for whitespace                               -->
-        <!-- See http://checkstyle.sf.net/config_whitespace.html -->
+        <!-- See https://checkstyle.org/config_whitespace.html -->
         <module name="EmptyForIteratorPad"/>
         <module name="GenericWhitespace"/>
         <module name="MethodParamPad"/>
@@ -137,12 +141,12 @@
         <module name="WhitespaceAround"/>
 
         <!-- Modifier Checks                                    -->
-        <!-- See http://checkstyle.sf.net/config_modifiers.html -->
+        <!-- See https://checkstyle.org/config_modifiers.html -->
         <module name="ModifierOrder"/>
         <module name="RedundantModifier"/>
 
         <!-- Checks for blocks. You know, those {}'s         -->
-        <!-- See http://checkstyle.sf.net/config_blocks.html -->
+        <!-- See https://checkstyle.org/config_blocks.html -->
         <module name="AvoidNestedBlocks"/>
         <module name="EmptyBlock"/>
         <module name="LeftCurly"/>
@@ -150,8 +154,7 @@
         <module name="RightCurly"/>
 
         <!-- Checks for common coding problems               -->
-        <!-- See http://checkstyle.sf.net/config_coding.html -->
-        <module name="AvoidInlineConditionals"/>
+        <!-- See https://checkstyle.org/config_coding.html -->
         <module name="EmptyStatement"/>
         <module name="EqualsHashCode"/>
         <!-- <module name="HiddenField"/> -->
@@ -159,22 +162,23 @@
         <module name="InnerAssignment"/>
         <module name="MagicNumber"/>
         <module name="MissingSwitchDefault"/>
+        <module name="MultipleVariableDeclarations"/>
         <module name="SimplifyBooleanExpression"/>
         <module name="SimplifyBooleanReturn"/>
 
         <!-- Checks for class design                         -->
-        <!-- See http://checkstyle.sf.net/config_design.html -->
-        <!--<module name="DesignForExtension"/>-->
+        <!-- See https://checkstyle.org/config_design.html -->
+        <!-- <module name="DesignForExtension"/> -->
         <module name="FinalClass"/>
         <module name="HideUtilityClassConstructor"/>
         <module name="InterfaceIsType"/>
         <module name="VisibilityModifier"/>
 
         <!-- Miscellaneous other checks.                   -->
-        <!-- See http://checkstyle.sf.net/config_misc.html -->
+        <!-- See https://checkstyle.org/config_misc.html -->
         <module name="ArrayTypeStyle"/>
         <module name="FinalParameters"/>
-        <!--<module name="TodoComment"/>-->
+        <!-- <module name="TodoComment"/> -->
         <module name="UpperEll"/>
 
     </module>