Added examples for Nullable/NotNull Annotations,

more/better PMD rules
spotbugs

pmd-ruleset.xml

@@ -0,0 +1,31 @@
+<?xml version="1.0" encoding="UTF-8"?>
+
+<ruleset name="Custom Java Ruleset"
+    xmlns="http://pmd.sourceforge.net/ruleset/2.0.0"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://pmd.sourceforge.net/ruleset/2.0.0 http://pmd.sourceforge.net/ruleset_2_0_0.xsd">
+
+    <description>
+        Custom ruleset for Java
+    </description>
+
+    <rule ref="category/java/bestpractices.xml">
+        <!-- System.println is ok in simple Console App -->
+        <exclude name="SystemPrintln" />
+    </rule>
+
+    <rule ref="category/java/codestyle.xml" />
+
+    <rule ref="category/java/design.xml" />
+
+    <rule ref="category/java/documentation.xml" />
+
+    <rule ref="category/java/errorprone.xml" />
+
+    <rule ref="category/java/multithreading.xml" />
+
+    <rule ref="category/java/performance.xml" />
+
+    <rule ref="category/java/security.xml" />
+
+</ruleset>

pom.xml

@@ -38,6 +38,7 @@
         <codehaus.version.plugin>2.11.0</codehaus.version.plugin>
         <spotbugs.maven.plugin>4.7.1.0</spotbugs.maven.plugin>
         <spotbugs.version>4.7.1</spotbugs.version>
+        <jetbrains.annotations.version>23.0.0</jetbrains.annotations.version>
 
         <!-- other properties -->
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
@@ -61,6 +62,14 @@
             <version>${junit.version}</version>
             <scope>test</scope>
         </dependency>
+
+        <!-- Dependency used for @NotNull / @Nullable -->
+        <dependency>
+            <groupId>org.jetbrains</groupId>
+            <artifactId>annotations</artifactId>
+            <version>${jetbrains.annotations.version}</version>
+            <scope>compile</scope>
+        </dependency>
     </dependencies>
 
     <build>
@@ -227,6 +236,18 @@
                         <version>${spotbugs.version}</version>
                     </dependency>
                 </dependencies>
+                <executions>
+                    <execution>
+                        <phase>prepare-package</phase>
+                        <goals>
+                            <!-- pmd does not stop build when violations are found -->
+                            <goal>spotbugs</goal>
+
+                            <!-- check stops the build when violations are found -->
+                            <!-- <goal>check</goal> -->
+                        </goals>
+                    </execution>
+                </executions>
             </plugin>
 
             <plugin>
@@ -265,8 +286,13 @@
                 </configuration>
                 <executions>
                     <execution>
+                        <phase>prepare-package</phase>
                         <goals>
-                            <goal>check</goal>
+                            <!-- pmd does not stop build when violations are found -->
+                            <goal>pmd</goal>
+
+                            <!-- check stops the build when violations are found -->
+                            <!-- <goal>check</goal> -->
                         </goals>
                     </execution>
                 </executions>

src/main/java/de/kneitzel/Greeting.java

@@ -0,0 +1,57 @@
+package de.kneitzel;
+
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+/**
+ * Simple Greeting class for some demonstration.
+ */
+public class Greeting {
+
+    /**
+     * Default name that should be greeted if no name is given.
+     */
+    public static final String DEFAULT_NAME = "Welt";
+
+    /**
+     * Name that should be greeted
+     * <p>
+     *     Cannot be null.
+     * </p>
+     */
+    @NotNull
+    private final String name;
+
+    /**
+     * Gets the name that should be greeted.
+     * @return Name that should be greeted.
+     */
+    public @NotNull String getName() {
+        return name;
+    }
+
+    /**
+     * Creates a new Instance of Greeting which greets the "World".
+     */
+    public Greeting() {
+        this(null);
+    }
+
+    /**
+     * Creates a new instance of Greeting to greet the given name.
+     * @param name Name that should be greeted by Greeting.
+     */
+    public Greeting(@Nullable final String name) {
+        this.name = name == null ? DEFAULT_NAME : name;
+    }
+
+    /**
+     * String representation of this instance.
+     * @return String representation of "Hello name!"
+     */
+    @NotNull
+    @Override
+    public String toString() {
+        return "Hallo " + name + "!";
+    }
+}

src/main/java/de/kneitzel/JavaApp.java

@@ -1,7 +1,23 @@
 package de.kneitzel;
 
-public class JavaApp {
-    public static void main(String[] args) {
-        System.out.println("Hello World!");
+import org.jetbrains.annotations.NotNull;
+
+/**
+ * Starting point of the JavaApp
+ */
+public final class JavaApp {
+
+    /**
+     * Provate Constructor - we never create an instance!
+     */
+    private JavaApp() {}
+
+    /**
+     * Entry point of the application.
+     * @param args Commandline parameters.
+     */
+    public static void main(@NotNull final String[] args) {
+        final Greeting greeting = new Greeting(null);
+        System.out.println(greeting);
     }
 }

src/main/java/module-info.java

@@ -1,2 +1,4 @@
 module AppModule {
+    // Jetbrains Dependency: @NotNull / @Nullable
+    requires org.jetbrains.annotations;
 }