Add checkstyle

.gitignore

@@ -3,22 +3,6 @@
 *.sh
 *.prefs
 
-### Maven ###
-/mvn
-/target/lib
-/target/maven-archiver
-/target/classes
-/target/maven-status
-pom.xml.tag
-pom.xml.releaseBackup
-pom.xml.versionsBackup
-pom.xml.next
-release.properties
-dependency-reduced-pom.xml
-buildNumber.properties
-.mvn/timing.properties
-out/
-
 ### Java ###
 *.class
 
@@ -128,7 +112,6 @@ local.properties
 # STS (Spring Tool Suite)
 .springBeans
 /target/
-checkstyle.xml
 classes/
 *.bat
 docs/

config/checkstyle/checkstyle.xml

@@ -0,0 +1,34 @@
+<?xml version="1.0"?>
+<!DOCTYPE module PUBLIC
+  "-//Checkstyle//DTD Checkstyle Configuration 1.3//EN"
+  "https://checkstyle.org/dtds/configuration_1_3.dtd">
+<module name="Checker">
+
+  <module name="FileTabCharacter">
+    <property name="eachLine" value="true"/>
+    <property name="severity" value="error"/>
+  </module>
+
+  <module name="TreeWalker">
+    <module name="FinalLocalVariable"/>
+    <module name="AvoidStarImport"/>
+    <module name="Indentation">
+      <property name="severity" value="ignore"/>
+    </module>
+  </module>
+
+  <module name="RegexpSingleline">
+    <property name="format" value="\borg\.junit\.jupiter\.api\.Assertions\.fail\s*\(\s*&quot;Not yet implemented&quot;\s*\)\s*;"/>
+    <property name="message" value="Remove placeholder fail() and implement the test."/>
+    <property name="ignoreCase" value="true"/>
+    <property name="severity" value="warning"/>
+  </module>
+
+  <module name="RegexpSingleline">
+    <property name="format" value="(?&lt;!\w)fail\s*\(\s*&quot;Not yet implemented&quot;\s*\)\s*;"/>
+    <property name="message" value="Remove placeholder fail() and implement the test."/>
+    <property name="severity" value="warning"/>
+  </module>
+
+</module>
+