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  1. interface Aggregate {
  2.   public abstract Iterator iterator();
  3. }
  4.  
  5. interface Iterator {
  6.   public abstract boolean hasNext();
  7.   public abstract Object next();
  8. }
  9.  
  10. class Book {
  11.   private String name ="";
  12.   public Book(String name) { this.name = name; }
  13.   public String getName() { return name; }
  14. }
  15.  
  16. class BookShelf implements Aggregate {
  17.   private java.util.ArrayList<Book> books;
  18.   public BookShelf(int maxsize) { /* constructor */
  19.     this.books = new java.util.ArrayList<Book>(maxsize);
  20.   }
  21.   Book getBookAt(int index) { /* called from iterator */
  22.     return books.get(index);
  23.   }
  24.   public int getLength() { return books.size(); } /* called from iterator */
  25.   public Iterator iterator() { /* called form iterator; make iterator */
  26.     return new BookShelfIterator(this);
  27.   }
  28.   public void appendBook(Book book) { /* utility for main */
  29.     this.books.add(book);
  30.   }
  31. }
  32.  
  33. class BookShelfIterator implements Iterator {
  34.   private BookShelf bookShelf;
  35.   private int index;
  36.  
  37.   public BookShelfIterator(BookShelf bookShelf) { /* constructor */
  38.     this.bookShelf = bookShelf;
  39.     this.index = 0;
  40.   }
  41.   public boolean hasNext() {
  42.     if (index < bookShelf.getLength()) return true;
  43.     else return false;
  44.   }
  45.   public Object next() {
  46.     Book book = bookShelf.getBookAt(index);
  47.     index++;
  48.     return book;
  49.   }
  50. }
  51.  
  52. class Main {
  53.   public static void main(String[] args) {
  54.     BookShelf bookShelf = new BookShelf(4);
  55.     bookShelf.appendBook(new Book("Around the World in 80 Days"));
  56.     bookShelf.appendBook(new Book("Bible"));
  57.     bookShelf.appendBook(new Book("Cinderella"));
  58.     bookShelf.appendBook(new Book("Daddy-Long-Legs"));    
  59.     bookShelf.appendBook(new Book("EinStein"));
  60.     bookShelf.appendBook(new Book("Faraday"));
  61.     Iterator it = bookShelf.iterator();
  62.     while (it.hasNext()) {
  63.       Book book = (Book)it.next();
  64.       System.out.println("" + book.getName());
  65.     }
  66.   }
  67. }
  68. /* end */
  69.  
Success #stdin #stdout 0.06s 2841600KB
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Around the World in 80 Days
Bible
Cinderella
Daddy-Long-Legs
EinStein
Faraday
https://ideone.com/DJ9pI5
language:
Java (HotSpot 12)
created:
8 years ago
visibility:
public

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