Added examples for Nullable/NotNull Annotations,

more/better PMD rules
spotbugs

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);
     }
 }