Enhance documentation for Greeting and JavaApp classes

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

@@ -2,51 +2,60 @@ package de.kneitzel;
 
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
+
 /**
- * Simple Greeting class for some demonstration.
+ * Simple greeting value object used for demonstration purposes.
+ *
+ * <p>Instances are immutable and encapsulate a single name that is used when generating
+ * a greeting string via {@link #toString()}.
  */
 public class Greeting {
 
     /**
-     * Default name that should be greeted if no name is given.
+     * Default name used when no explicit name is provided. The default value is the German
+     * word {@code "Welt"} ("world").
      */
     public static final String DEFAULT_NAME = "Welt";
 
     /**
-     * Name that should be greeted
-     * <p>
-     *     Cannot be null.
-     * </p>
+     * The name to greet. Never {@code null}.
      */
     @NotNull
     private final String name;
 
     /**
-     * Gets the name that should be greeted.
-     * @return Name that should be greeted.
+     * Returns the name that will be greeted.
+     *
+     * @return the name to greet; never {@code null}.
      */
     public @NotNull String getName() {
         return name;
     }
 
     /**
-     * Creates a new Instance of Greeting which greets the "World".
+     * Creates a new {@code Greeting} instance that greets the default name ({@link #DEFAULT_NAME}).
      */
     public Greeting() {
         this(null);
     }
 
     /**
-     * Creates a new instance of Greeting to greet the given name.
-     * @param name Name that should be greeted by Greeting.
+     * Creates a new {@code Greeting} instance for the given name.
+     *
+     * @param name the name to greet; may be {@code null} in which case {@link #DEFAULT_NAME}
+     *             will be used instead.
      */
     public Greeting(@Nullable final String name) {
         this.name = name == null ? DEFAULT_NAME : name;
     }
 
     /**
-     * String representation of this instance.
-     * @return String representation of "Hello name!"
+     * Returns a greeting string for this instance.
+     *
+     * <p>The greeting is formatted in German as {@code "Hallo <name>!"}. The returned string is
+     * never {@code null}.
+     *
+     * @return a greeting such as {@code "Hallo Welt!"}; never {@code null}.
      */
     @NotNull
     @Override