IteratorPatternTest.java

package Iterator_Pattern;

import java.util.Iterator;

public class IteratorPatternTest {
    public static void main(String[] args) {
        BookShelf bookShelf = new BookShelf(4);
        bookShelf.appendBook(new Book("Around the World in 80 Days"));
        bookShelf.appendBook(new Book("Bible"));
        bookShelf.appendBook(new Book("Cinderella"));
        bookShelf.appendBook(new Book("Daddy-Long-Legs"));

        Iterator<Book> it = bookShelf.iterator();
        while (it.hasNext()) {
            Book book = it.next();
            System.out.println(book.getName());
        }
        System.out.println();

        for(Book book : bookShelf) {
            System.out.println(book.getName());
        }
        System.out.println();
    }
}

class Book {
    private String name;

    public Book(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }
}

class BookShelf implements Iterable<Book> {
    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;
    }

    @Override
    public Iterator<Book> iterator() {
        return new BookShelfIterator(this);
    }
}

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;
        } else {
            return false;
        }
    }

    @Override
    public Book next() {
        if (!hasNext()) {
            throw new java.util.NoSuchElementException();
        }
        Book book = bookShelf.getBookAt(index);
        index++;
        return book;
    }
}