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Commit 19beb80

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🎉 iterator pattern
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---
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title: Java设计模式之Iterator模式
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date: 2019年09月02日 21:50:06
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tags: [Java,design and pattern]
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---
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## 学习笔记 : Java设计模式之Iterator模式
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### 概述
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*迭代器模式 : 提供一种方法顺序访问一个聚合对象中的各个元素,而又不暴露该对象的内部表示. 迭代器模式又称( Cursor )模式,它是一种对象行为型模式( Iterator Pattern : Provide a way to access the elements of an aggregate object sequentially without exposing its underlying representation )*
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### 示例程序-详细版
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*下面是一个实现了`Iterator模式`的示例程序,其作用是将书籍信息( Book )放到存储书籍信息的书架( BookSelf )上,并将书的名字按顺序显示出来*
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1. *Book : 图书信息类*
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```java
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package pers.huangyuhui.iterator;
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/**
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* @project: design-patterns
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* @description: Book信息
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* @author: 黄宇辉
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* @date: 9/2/2019-4:59 PM
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* @version: 1.0
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* @website: https://yubuntu0109.github.io/
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*/
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public class Book {
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private String name;
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public Book(String name) {
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this.name = name;
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}
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public String getName() {
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return name;
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}
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}
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```
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2. *Aggregate接口 : 充当集合角色*
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```java
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package pers.huangyuhui.iterator;
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/**
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* @project: design-patterns
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* @description: 集合
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* @author: 黄宇辉
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* @date: 9/2/2019-5:00 PM
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* @version: 1.0
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* @website: https://yubuntu0109.github.io/
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*/
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public interface Aggregate {
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Iterator iterator();
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}
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```
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3. *BookSelf类 : 充当具体的集合角色*
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```java
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package pers.huangyuhui.iterator;
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/**
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* @project: design-patterns
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* @description: 具体的集合
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* @author: 黄宇辉
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* @date: 9/2/2019-5:03 PM
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* @version: 1.0
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* @website: https://yubuntu0109.github.io/
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*/
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public class BookSelf implements Aggregate {
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private Book[] books;
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private int last = 0;
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public BookSelf(int maxsize) {
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this.books = new Book[maxsize];
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}
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public Book getBookByIndex(int index) {
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return books[index];
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}
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public void appendBook(Book book) {
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this.books[last++] = book;
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}
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public int getLength() {
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return last;
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}
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@Override
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public Iterator iterator() {
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return new BookShelfIterator(this);
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}
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}
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```
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4. *Iterator接口 : 充当迭代器角色*
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```java
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package pers.huangyuhui.iterator;
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/**
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* @project: design-patterns
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* @description: 迭代器
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* @author: 黄宇辉
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* @date: 9/2/2019-5:01 PM
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* @version: 1.0
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* @website: https://yubuntu0109.github.io/
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*/
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public interface Iterator {
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boolean hasNext();
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Object next();
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}
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```
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5. *BookShelfIterator类 : 充当具体的迭代器角色*
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```java
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package pers.huangyuhui.iterator;
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/**
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* @project: design-patterns
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* @description: 集体的迭代器
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* @author: 黄宇辉
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* @date: 9/2/2019-5:07 PM
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* @version: 1.0
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* @website: https://yubuntu0109.github.io/
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*/
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public class BookShelfIterator implements Iterator {
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private BookSelf bookSelf;
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private int index;
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public BookShelfIterator(BookSelf bookSelf) {
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this.bookSelf = bookSelf;
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this.index = 0;
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}
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@Override
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public boolean hasNext() {
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return index < bookSelf.getLength();
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}
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@Override
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public Object next() {
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return bookSelf.getBookByIndex(index++);
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}
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}
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```
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6. *Test测试类*
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```java
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package pers.huangyuhui.iterator;
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/**
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* @project: design-patterns
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* @description: 测试类
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* @author: 黄宇辉
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* @date: 9/2/2019-5:09 PM
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* @version: 1.0
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* @website: https://yubuntu0109.github.io/
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*/
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public class Test {
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//demo
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public static void main(String[] args) {
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BookSelf bookSelf = new BookSelf(5);
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bookSelf.appendBook(new Book("A-BOOK"));
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bookSelf.appendBook(new Book("B-BOOK"));
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bookSelf.appendBook(new Book("C-BOOK"));
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bookSelf.appendBook(new Book("D-BOOK"));
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bookSelf.appendBook(new Book("E-BOOK"));
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Iterator iterator = bookSelf.iterator();
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while (iterator.hasNext()) {
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Book book = (Book) iterator.next();
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System.out.println(book.getName());
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}
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}
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}
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```
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7. *程序运行结果如下所示 :*
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```
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A-BOOK
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B-BOOK
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C-BOOK
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D-BOOK
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E-BOOK
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```
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#### 示例程序的类图
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![ ](https://raw.githubusercontent.com/YUbuntu0109/YUbuntu0109.github.io/HexoBackup/source/_posts/Java%E8%AE%BE%E8%AE%A1%E6%A8%A1%E5%BC%8F%E4%B9%8BIterator-Pattern/Iterator1-ClassDiagram.png)
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#### Iterator模式中的角色分析
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* `Iterator( 迭代器 )` : 该角色负责定义按顺序逐个遍历元素的接口( API ),在上述程序中,由`Iterator接口`扮演此角色.
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* `ConcreteIterator( 具体的迭代器 )` : 该角色负责实现`Iterator角色`所定义的接口( API ). 在上述程序中,由`BookShelfIterator类`扮演此角色.
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* `Aggregate( 集合 / 抽象聚合类 )` : 该角色负责定义创建`Iterator角色`的接口( API ),在上述程序中,由`Aggregate接口`扮演此角色.
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* `ConcreteAggregate( 具体的集合 / 具体聚合类 )` : 该角色负责实现`Aggregate角色`所定义的接口( API ),它会创建出具体的`Iterator角色`. 在上述程序中,由`BookSelf类`扮演了此角色.
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### 示例程序-简洁版
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*下面同样是一个实现了`Iterator模式`的示例程序( 同上 ),其作用是将商品数据存储到商品集合( ProductList )中,并将商品的名字按顺序显示出来*
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1. *AbstractObjectList : 抽象聚合类*
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```java
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package pers.huangyuhui.iterator2;
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import java.util.List;
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/**
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* @project: design-patterns
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* @description: 抽象聚合类
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* @author: 黄宇辉
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* @date: 9/2/2019-5:51 PM
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* @version: 1.0
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* @website: https://yubuntu0109.github.io/
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*/
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public abstract class AbstractObjectList {
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protected List<Object> objects;
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public AbstractObjectList(List<Object> objects) {
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this.objects = objects;
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}
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public void addObject(Object object) {
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this.objects.add(object);
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}
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public void removeObject(Object object) {
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this.objects.remove(object);
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}
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public List<Object> getObjects() {
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return objects;
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}
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//创建迭代器的抽象工厂方法
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public abstract AbstractIterator iterator();
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}
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```
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2. *ProductList : 商品数据类,充当具体聚合类. ProductIterator(内部类) : 商品迭代器,充当具体迭代器*
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```java
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package pers.huangyuhui.iterator2;
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import java.util.List;
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/**
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* @project: design-patterns
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* @description: 商品书籍类, 充当具体聚合类
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* @author: 黄宇辉
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* @date: 9/2/2019-5:56 PM
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* @version: 1.0
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* @website: https://yubuntu0109.github.io/
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*/
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public class ProductList extends AbstractObjectList {
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public ProductList(List<Object> objects) {
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super(objects);
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}
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@Override
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public AbstractIterator iterator() {
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return new ProductIterator();
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}
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/*
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ProductIterator:商品迭代器,充当具体迭代器(使用内部类实现迭代器,与jdk中的迭代器实现原理相同)
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*/
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public class ProductIterator implements AbstractIterator {
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private int cursor;
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public ProductIterator() {
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cursor = 0;
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}
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@Override
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public boolean hasNext() {
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return cursor < objects.size();
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}
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@Override
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public Object next() {
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return objects.get(cursor++);
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}
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}
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}
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```
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3. *AbstractIterator : 抽象迭代器*
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```java
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package pers.huangyuhui.iterator2;
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/**
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* @project: design-patterns
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* @description: 抽象迭代器
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* @author: 黄宇辉
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* @date: 9/2/2019-5:55 PM
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* @version: 1.0
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* @website: https://yubuntu0109.github.io/
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*/
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public interface AbstractIterator {
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boolean hasNext();
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Object next();
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}
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```
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4. *Test : 测试类*
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```java
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package pers.huangyuhui.iterator2;
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import java.util.ArrayList;
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import java.util.List;
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/**
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* @project: design-patterns
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* @description: 测试类
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* @author: 黄宇辉
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* @date: 9/2/2019-6:13 PM
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* @version: 1.0
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* @website: https://yubuntu0109.github.io/
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*/
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public class Test {
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//demo
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public static void main(String[] args) {
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List<Object> arrayList = new ArrayList<>();
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arrayList.add("A-BOOK");
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arrayList.add("B-BOOK");
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arrayList.add("C-BOOK");
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ProductList productList = new ProductList(arrayList);
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productList.addObject("D-BOOK");
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productList.addObject("E-BOOK");
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productList.removeObject("A-BOOK");
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AbstractIterator iterator = productList.iterator();
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while (iterator.hasNext()) {
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System.out.println(iterator.next());
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}
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System.out.println("all datas : " + productList.getObjects().toString());
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}
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}
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```
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5. *程序运行结果如下所示 :*
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```
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B-BOOK
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C-BOOK
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D-BOOK
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E-BOOK
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all datas : [B-BOOK, C-BOOK, D-BOOK, E-BOOK]
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```
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#### 示例程序的类图
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![ ](https://raw.githubusercontent.com/YUbuntu0109/YUbuntu0109.github.io/HexoBackup/source/_posts/Java%E8%AE%BE%E8%AE%A1%E6%A8%A1%E5%BC%8F%E4%B9%8BIterator-Pattern/Iterator2-ClassDiagram.png)
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*📚参与书籍 : 《图解设计模式 - [日]结诚浩 · 著》, 《Java设计模式 - 刘伟编 · 著》*
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package pers.huangyuhui.iterator_pattern.iterator1;
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/**
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* @project: design-patterns
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* @description: 集合
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* @author: 黄宇辉
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* @date: 9/2/2019-5:00 PM
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* @version: 1.0
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* @website: https://yubuntu0109.github.io/
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*/
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public interface Aggregate {
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Iterator iterator();
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}

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