Java 设计模计之(一)—— 迭代器(Iterator pattern)

1. 角色

2. Sample:

代码一:

public interface Aggregate {
    public abstract Iterator iterator();
}

代码二：

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

代码三：

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

代码四:

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

代码五：

public class BookShelfIterator implements Iterator {
    private BookShelf bookShelf;
    private int index;
    public BookShelfIterator(BookShelf bookShelf){
        this.bookShelf = bookShelf;
        this.index = 0;
    }
    @Override
    public boolean hasNext() {
        // TODO Auto-generated method stub
        if (index < bookShelf.getLength()) {
            return true;
        } else {
            return false;
        }
    }

    @Override
    public Object next() {
        // TODO Auto-generated method stub
        Book book = bookShelf.getBookAt(index);
        index++;
        return book;
    }

}

代码六：

public class Main {
    public static void main(String[] args) {
        BookShelf bookShelf = new BookShelf(4);
        bookShelf.appendBook(new Book("Thinking in java"));
        bookShelf.appendBook(new Book("Thinking in Action"));
        bookShelf.appendBook(new Book("Java design pattern"));
        bookShelf.appendBook(new Book("UML design pattern"));
        Iterator it = bookShelf.iterator();
        while (it.hasNext()){
            Book book = (Book)it.next();
            System.out.println(""+ book.getName());
        }
    }

}