checkstyle.xml: add 3 modules

Author: stephengold

config/checkstyle/checkstyle.xml

@@ -146,6 +146,11 @@
         <!-- Miscellaneous checks:                  -->
         <!-- See https://checkstyle.org/checks/misc -->
         <module name="ArrayTypeStyle"/>
+        <module name="AvoidEscapedUnicodeCharacters">
+            <property name="allowByTailComment" value="true"/>
+            <property name="allowEscapesForControlCharacters" value="true"/>
+            <property name="allowNonPrintableEscapes" value="true"/>
+        </module>
         <module name="CommentsIndentation">
             <property name="tokens" value="SINGLE_LINE_COMMENT, BLOCK_COMMENT_BEGIN"/>
         </module>
@@ -230,6 +235,13 @@
             <message key="name.invalidPattern" value="Type name ''{0}'' must match pattern ''{1}''."/>
         </module>
 
+        <!-- Regexp checks:                           -->
+        <!-- See https://checkstyle.org/checks/regexp -->
+        <module name="RegexpSinglelineJava">
+            <property name="format" value="\{[ ]+\}"/>
+            <property name="message" value="Empty blocks should have no spaces. Empty blocks may only be represented as '{}' when not part of a multi-block statement (4.1.3)"/>
+        </module>
+
         <!-- Checks for size violations:             -->
         <!-- See https://checkstyle.org/checks/sizes -->
         <module name="MethodLength">
@@ -241,6 +253,7 @@
 
         <!-- Checks for whitespace:                       -->
         <!-- See https://checkstyle.org/checks/whitespace -->
+        <module name="EmptyForInitializerPad"/>
         <module name="EmptyForIteratorPad"/>
         <module name="EmptyLineSeparator">
             <property name="allowNoEmptyLineBetweenFields" value="true"/>