每天一个设计模式之迭代器模式（Iterator Pattern）

一、UML类图

二、代码示例

Container角色

public interface BookCollection extends Iterable<Book> {
    Iterator<Book> iterator();
}

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Container具体类

public class BookLibrary implements BookCollection {
    private Collection<Book> books;

    public BookLibrary(Collection<Book> books) {
        this.books = books;
    }

    public boolean addBook(Book book) {
        return books.add(book);
    }

    public Collection<Book> getBooks() {
        return books;
    }

    public Iterator<Book> iterator() {
        return books.iterator();
    }
}
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测试

public class Client {
    public static void main(String[] args) {
        Book[] books = new Book[5];
        books[0] = new Book("English", "Head First Java, 2nd Edition", "Kathy Sierra", 10123758943l, 10.5d);
        books[1] = new Book("English", "Effective Java (3rd Edition)", "Bloch Joshua", 34422235432l, 8.65d);
        books[2] = new Book("English", "Mastering Java Machine Learning", "Dr Uday Kamath", 2123765476l, 21.45d);
        books[3] = new Book("English", "Cloud-Native Java", "Kenny Bastani ", 21332343434l, 28.99d);
        books[4] = new Book("English", "Java 9 Modularity", "Paul Bakker", 1645243587l, 36.68d);

        BookLibrary bookLibrary = new BookLibrary(Arrays.asList(books));
        for (Book book : bookLibrary) {
            System.out.println(book);
        }
    }
}
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运行结果

Book{language='English', title='Head First Java, 2nd Edition', author='Kathy Sierra', ISBN=10123758943, price=10.5}
Book{language='English', title='Effective Java (3rd Edition)', author='Bloch Joshua', ISBN=34422235432, price=8.65}
Book{language='English', title='Mastering Java Machine Learning', author='Dr Uday Kamath', ISBN=2123765476, price=21.45}
Book{language='English', title='Cloud-Native Java', author='Kenny Bastani ', ISBN=21332343434, price=28.99}
Book{language='English', title='Java 9 Modularity', author='Paul Bakker', ISBN=1645243587, price=36.68}

Process finished with exit code 0
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三、参考

1. https://www.runoob.com/design-pattern/iterator-pattern.html
2. https://www.geeksforgeeks.org/design-patterns-in-java-iterator-pattern/
3. https://www.digitalocean.com/community/tutorials/iterator-design-pattern-java