反復器モード【ITERATOR PATTERN】

public class Book
{
    private String name;
    
    public Book(String name)
    {
        this.name = name;
    }
    
    public String getName()
    {
        return name;
    }
    
    public static void main(String[] args)
    {
        BookShelf bookShelf = new BookShelf(3);
        bookShelf.appendBook(new Book("Around the World in 80 Days"));
        bookShelf.appendBook(new Book("Bible"));
        bookShelf.appendBook(new Book("Cinderella"));
        Iterator it = bookShelf.iterator();
        while (it.hasNext())
        {
            Book book = (Book)it.next();
            System.out.println("" + book.getName());
        }
    }
}

interface Aggregate
{
    public abstract Iterator iterator();
}

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 iterator()
    {
        return new BookShelfIterator(this);
    }
}

interface Iterator
{
    public abstract boolean hasNext();
    
    public abstract Object next();
}

class BookShelfIterator implements Iterator
{
    private BookShelf bookShelf;
    
    private int index;
    
    public BookShelfIterator(BookShelf bookShelf)
    {
        this.bookShelf = bookShelf;
        this.index = 0;
    }
    
    public boolean hasNext()
    {
        if (index < bookShelf.getLength())
        {
            return true;
        }
        else
        {
            return false;
        }
    }
    
    public Object next()
    {
        Book book = bookShelf.getBookAt(index);
        index++;
        return book;
    }
}