Aggregate.java

import java.util.Iterator;

public interface Aggregate {
	public abstract Iterator<Book> iterator();
}

Book.java

public class Book {
	private String name;
	
	public Book(String name) {
		this.name = name;
	}
	
	public String getName(){
		return this.name;
	}
}

BookShelf.java

import java.util.Iterator;

public class BookShelf implements Aggregate{
	private Book[] books;
	private int last = 0;
	
	public BookShelf(int maxsize) {
		this.books = new Book[maxsize];
	}
	
	public Book getBookAt(int index){
		return books[index];
	}
	public void appendBook(Book book){
		this.books[last] = book;
		last++;
	}
	public int getLength(){
		return last;
	}
	public Iterator<Book> iterator(){
		return new BookShelfIterator(this);
	}
}

BookShelfIterator.java

import java.util.Iterator;

public class BookShelfIterator implements Iterator<Book> {
	private BookShelf bookShelf;
	private int index;
	
	public BookShelfIterator(BookShelf bookShelf) {
		this.bookShelf = bookShelf;
		this.index = 0;
	}
	@Override
	public boolean hasNext() {
		if(index < bookShelf.getLength()){
			return true;
		}
		return false;
	}

	@Override
	public Book next() {
		Book book = bookShelf.getBookAt(index);
		index++;
		return book;
	}

	@Override
	public void remove() {

	}

}