import java.util.*;

public class BookDemo {

public static void main(String[] args) {

Book book = new Book();

book.add(new Chapter("Chapter 1"));

book.add(new Chapter("Chapter 2"));

book.add(new Chapter("Chapter 3"));

for(Chapter ch : book) {

System.out.println(ch);

}

}

}

class Book implements Iterable<Chapter> {

private List<Chapter> chapters = new ArrayList<>();

public void add(Chapter chapter) {

this.chapters.add(chapter);

}

@Override

public Iterator<Chapter> iterator() {

return chapters.iterator();

}

}

class Chapter {

private String title;

public Chapter(String title) {

this.title = title;

}

@Override

public String toString() {

return this.title;

}

}