【设计模式-迭代器模式】

设计模式-迭代器模式

迭代器接口，至少需要两个方法：hasNext、next：

package com.javaxiang.pattern.iterator;

/**
 * @author Created by li'xiang on 2021/12/27 17:44
 */
public interface Iterator<E> {

    /**
     * 是否有元素
     */
    boolean hasNext();

    /**
     * 返回下一个元素
     */
    E next();

}

一个集合类，我们以遍历书架 BookShelf 上的书籍 Book 来举例

Book类：只有一个属性：书名

package com.javaxiang.pattern.iterator;

/**
 * @author Created by li'xiang on 2021/12/27 17:46
 */
public class Book {
    private String name;

    public String getName() {
        return name;
    }

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

书架类 BookShelf 需要持有书籍 Book 的引用，并且实现 Iterator 接口

package com.javaxiang.pattern.iterator;


/**
 * @author Created by li'xiang on 2021/12/27 17:47
 */
public class BookShelf implements Iterator<Book> {

    private Book[] books;
    private int index, last;

    public BookShelf(int maxSize) {
        this.books = new Book[maxSize];
    }

    public void addBook(Book book){
        this.books[last++] = book;
    }


    /**
     * 是否有元素
     */
    @Override
    public boolean hasNext() {
        return index < last;
    }

    /**
     * 返回下一个元素
     */
    @Override
    public Book next() {
        return this.books[index++];
    }
}

测试类：

package com.javaxiang.pattern.iterator;

import lombok.extern.slf4j.Slf4j;

/**
 * @author Created by li'xiang on 2021/12/27 18:13
 */
@Slf4j
public class Main {

    public static void main(String[] args) {
        BookShelf bookShelf = new BookShelf(5);
        bookShelf.addBook(new Book("西游记"));
        bookShelf.addBook(new Book("三国演义"));
        bookShelf.addBook(new Book("红楼梦"));
        bookShelf.addBook(new Book("水浒传"));

        while (bookShelf.hasNext()){
            Book book = bookShelf.next();
            log.info("book name = {}", book.getName());
        }
    }
}

测试结果：

18:38:46.245 [main] INFO com.javaxiang.pattern.iterator.Main - book name = 西游记
18:38:46.248 [main] INFO com.javaxiang.pattern.iterator.Main - book name = 三国演义
18:38:46.248 [main] INFO com.javaxiang.pattern.iterator.Main - book name = 红楼梦
18:38:46.248 [main] INFO com.javaxiang.pattern.iterator.Main - book name = 水浒传