Added code to demo expected package error (#11045)

* Added code for demo package error

* Corrected the package declaration

* BAEL-4216 Corrected Formatting and Removed final and Super

* Added few comments as per PR

* Update Book.java

Formatted comments with spaces

Co-authored-by: ine12363914 <saikat.chakraborty@tesco.com>

core-java-modules/core-java-lang-4/src/main/java/com/baeldung/bookstore/Book.java

@@ -0,0 +1,21 @@
+// The next line is commented out to avoid the code to fail the build.
+// package com.baeldung;
+
+/**
+* If the below package declaration is commented out and the above incorrect package 
+* declaration is uncommented, then the problem will replicate.
+*/
+package com.baeldung.bookstore;
+
+public class Book {
+
+    private String title;
+    private String author;
+    private long isbn;
+    
+    public Book(String title, String author, long isbn) {
+        this.title = title;
+        this.author = author;
+        this.isbn = isbn;
+    }
+}

core-java-modules/core-java-lang-4/src/main/java/com/baeldung/bookstore/LibraryAdmin.java

@@ -0,0 +1,14 @@
+package com.baeldung.bookstore;
+
+import java.util.Random;
+
+public class LibraryAdmin {
+
+    public Book createBook(String title, String author) {
+
+        final long isbn = new Random().nextLong();
+
+        return new Book(title, author, isbn);
+    }
+    
+}