Introduction of checkstyle

.github/workflows/checkstyle.yml

@@ -0,0 +1,37 @@
+name: checkstyle
+
+on:
+    push:
+        branches:
+            - master
+            - 'dev/**'
+    pull_request:
+
+jobs:
+    build:
+        if: "! contains(toJSON(github.event.commits.*.message), '[ci skip]')"
+        runs-on: ubuntu-latest
+        steps:
+            - uses: actions/checkout@v4
+              with:
+                  submodules: recursive
+            - name: validate gradle wrapper
+              uses: gradle/wrapper-validation-action@v2
+            - name: Set up JDK 21
+              uses: actions/setup-java@v4
+              with:
+                  java-version: '21'
+                  distribution: 'adopt'
+                  cache: gradle
+            - name: Grant execute permission for gradlew
+              run: chmod +x gradlew
+            - name: Run checkstyle
+              run: ./gradlew clean checkstyleMain
+            - name: Upload checkstyle report
+              uses: actions/upload-artifact@v4
+              if: success()
+              with:
+                  name: checkstyle-report
+                  path: |
+                    build/reports/checkstyle/*.xml
+                    build/reports/checkstyle/*.html

build.gradle

@@ -7,6 +7,7 @@ plugins {
 	id 'com.github.johnrengelman.shadow' version '8.1.1'
 	id 'maven-publish'
 	id 'java'
+	id 'checkstyle'
 }
 
 configurations {
@@ -42,6 +43,11 @@ dependencies {
 	testShadow group: 'org.easymock', name: 'easymock', version: '5.4.0'
 }
 
+checkstyle {
+	configFile = new File("checkstyle.xml")
+	sourceSets = [] // disables checkstyle after build task
+}
+
 task checkAliases {
 	description 'Checks for the existence of the aliases.'
 	doLast {

checkstyle.xml

@@ -0,0 +1,100 @@
+<?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">
+
+	<!--Basic Settings-->
+	<!--Warning severity so the builds do not fail because of checkstyle, this is mainly for the GitHub workflow-->
+	<property name="severity" value="warning"/>
+	<property name="fileExtensions" value="java"/>
+	<module name="BeforeExecutionExclusionFileFilter">
+		<property name="fileNamePattern" value="module\-info\.java$"/>
+	</module>
+
+	<!--At most 120 characters per line-->
+	<module name="LineLength">
+		<property name="max" value="120"/>
+	</module>
+
+	<!--New line at the end of the file-->
+	<module name="NewlineAtEndOfFile"/>
+
+	<module name="TreeWalker">
+
+		<!--Tabs, no spaces-->
+		<module name="RegexpSinglelineJava">
+			<property name="format" value="^\t* "/>
+			<property name="message" value="Indent must use tab characters"/>
+			<property name="ignoreComments" value="true"/>
+		</module>
+
+		<!--No trailing whitespace-->
+		<module name="NoWhitespaceAfter" />
+
+		<!--When statements consume multiple lines, all lines but the first have two tabs of additional indentation-->
+		<module name="Indentation">
+			<property name="arrayInitIndent" value="8" />
+			<property name="basicOffset" value="8" />
+			<property name="caseIndent" value="8" />
+			<property name="lineWrappingIndentation" value="8" />
+			<property name="throwsIndent" value="8" />
+		</module>
+
+		<!--Each class begins with an empty line-->
+		<module name="EmptyLineSeparator">
+			<property name="allowNoEmptyLineBetweenFields" value="true" />
+			<property name="tokens"
+					  value="IMPORT, STATIC_IMPORT, CLASS_DEF, INTERFACE_DEF,
+					  		ENUM_DEF, STATIC_INIT, INSTANCE_INIT, METHOD_DEF,
+					  		CTOR_DEF, VARIABLE_DEF, RECORD_DEF, COMPACT_CTOR_DEF" />
+		</module>
+
+		<module name="OneStatementPerLine"/>
+
+		<!--Annotations for a structure go on the line before that structure-->
+		<module name="AnnotationLocation"/>
+
+		<!--When splitting Strings into multiple lines the last part of the string must be (space character included) " " +-->
+		<module name="OperatorWrap">
+			<property name="option" value="eol" />
+			<property name="tokens" value="PLUS" />
+		</module>
+
+		<!--Class names are written in UpperCamelCase-->
+		<module name="TypeName"/>
+
+		<!--Methods named in camelCase-->
+		<module name="MethodName"/>
+
+		<!--Static constant fields should be named in UPPER_SNAKE_CASE-->
+		<module name="ConstantName"/>
+
+		<!--We use JetBrains Annotations for specifying null-ness-->
+		<module name="IllegalImport">
+			<property name="illegalClasses"
+					  value="javax.annotation.Nonnull,
+							javax.annotation.Nullable,
+							org.eclipse.jdt.annotation.NonNull,
+							org.eclipse.jdt.annotation.Nullable,
+							org.eclipse.sisu.Nullable,
+							org.checkerframework.checker.nullness.qual.NonNull,
+							org.checkerframework.checker.nullness.qual.Nullable" />
+			<property name="illegalPkgs" value="" />
+		</module>
+
+		<!--Modules for code improvements-->
+		<module name="MissingOverride"/>
+		<module name="EmptyBlock"/>
+		<module name="HideUtilityClassConstructor"/>
+		<module name="EmptyStatement"/>
+		<module name="EqualsHashCode"/>
+		<module name="SimplifyBooleanExpression"/>
+		<module name="SimplifyBooleanReturn"/>
+		<module name="StringLiteralEquality"/>
+		<module name="UnusedLocalVariable"/>
+
+	</module>
+
+</module>

code-conventions.md

@@ -97,6 +97,7 @@ If we need to remove or alter contributed code due to a licensing issue we will
 	- The exception to this is breaking up conditional statements (e.g. `if (x || y)`) where the
     condition starts may be aligned
 * Each class begins with an empty line
+* Each Java file ends with an empty line
 * No squeezing of multiple lines of code on a single line
 * Separate method declarations with empty lines
   	- Empty line after last method in a class is *not* required