I have a Super Class Book. I compile the Book.java and Book.class was generated succesfull.
But, when I make the sub Classes ChildrenBook.java and TechnicalBook.java the following mistake occur:

ChildrenBook.java:3: cannot resolve symbol
symbol : class Book
location: class com.wrox.library.ChildrenBook
public class ChildrenBook extends Book {
                                  ^
1 error

I have the 3 classes (Book, ChildrenBook, TechnicalBook) in the same folder.

What is the problem ?

There are two method:
1. import your book.class
2. javac *.java or make you classes in classpath