一、简介

1、定义

  迭代器模式(Iterator Pattern)是一种面向集合对象而生的行为设计模式。对于集合对象而言，会涉及对集合的添加和删除操作，也要支持遍历集合元素的操作。可以把遍历操作放在集合对象中，但这样做，集合对象就承担太多的责任了。面向对象设计原则中有一条就是单一职责原则，所以要尽可能地分离这些职责，用不同的类承担不同的责任，迭代器模式就是用迭代器类来承担遍历集合的职责。
  迭代器模式提供了一种方法顺序访问一个集合对象中的各个元素，而又无需暴露该集合对象的内部实现，这样既可以做到不暴露集合对象的内部结构，又可让外部代码透明地访问集合内部的数据。

2、命令模式的结构

迭代模式涉及以下几个角色：
迭代器（Iterator）接口：定义访问和遍历集合元素的抽象方法，通常包含 hasNext()、next() 等方法。
具体迭代器（Concretelterator）类：实现迭代器接口中所定义的方法，完成对集合对象的遍历，记录遍历的当前位置。
聚合（Aggregate）类：构建集合数据，返回一个具体迭代器的实例。
客户端（Client）类：调用聚合类，维护集合对象，通过迭代器遍历集合对象。

二、Java实现案例

1、概念实现案例

/*** @Description: 迭代器接口* @Date: 2025-01-10 10:41* @Author: gaoyufei**/
public interface Iterator {boolean hasNext();Object next();
}import java.util.List;
/*** @Description: 具体迭代器类* @Date: 2025-01-10 10:42* @Author: gaoyufei**/
public class ConcreteIterator implements Iterator{private List<Object> items;private int position;public ConcreteIterator(List<Object> items){this.items=items;}@Overridepublic boolean hasNext() {return position<items.size();}@Overridepublic Object next() {return items.get(position++);}
}import java.util.ArrayList;
import java.util.List;
/*** @Description: 聚合类* @Date: 2025-01-10 10:46* @Author: gaoyufei**/
public class Aggregate {private List<Object> items=new ArrayList<>();public void add(Object item){items.add(item);}public Iterator iterator(){return new ConcreteIterator(items);}
}/*** @Description: 客户端* @Date: 2025-01-10 10:48* @Author: gaoyufei**/
public class Client {public static void main(String[] args) {Aggregate aggregate=new Aggregate();aggregate.add("item 1");aggregate.add("item 2");Iterator iterator = aggregate.iterator();while (iterator.hasNext()){System.out.println(iterator.next());}}
}

2、书架遍历案例

/*** @Description: 书* @Date: 2025-01-10 13:07* @Author: gaoyufei**/
public class Book {private String name;public Book(String name){this.name=name;}public String getName() {return name;}public void setName(String name) {this.name = name;}
}/*** @Description: 迭代器接口* @Date: 2025-01-10 13:08* @Author: gaoyufei**/
public interface Iterator<E> {boolean hasNext();E next();
}/*** @Description: 书架迭代器类* @Date: 2025-01-10 13:10* @Author: gaoyufei**/
public class BookShelfIterator implements Iterator{private BookShelf bookShelf;private int index;public BookShelfIterator(BookShelf bookShelf){this.bookShelf=bookShelf;this.index=0;}@Overridepublic boolean hasNext() {return index<bookShelf.getBooks().size();}@Overridepublic Book next() {return bookShelf.getBooks().get(index++);}
}import java.util.ArrayList;
import java.util.List;
/*** @Description: 书架（聚合类）* @Date: 2025-01-10 13:12* @Author: gaoyufei**/
public class BookShelf {private List<Book> books=new ArrayList<>();public void add(Book book){books.add(book);}public List<Book> getBooks() {return books;}public void setBooks(List<Book> books) {this.books = books;}public Iterator iterator(){return new BookShelfIterator(this);}
}/*** @Description: 客户端* @Date: 2025-01-10 13:14* @Author: gaoyufei**/
public class Client {public static void main(String[] args) {BookShelf bookShelf=new BookShelf();bookShelf.add(new Book("思考致富"));bookShelf.add(new Book("思考，快与慢"));Iterator iterator = bookShelf.iterator();while (iterator.hasNext()){Book book = (Book)iterator.next();System.out.println(book.getName());}}
}

3、班级学生遍历案例

import java.util.Objects;/*** @Description: 学生类* @Date: 2025-01-10 13:42* @Author: gaoyufei**/
public class Student {private String name;public Student(String name) {this.name = name;}public String getName() {return name;}public void setName(String name) {this.name = name;}@Overridepublic boolean equals(Object o) {if (this == o) return true;if (o == null || getClass() != o.getClass()) return false;Student student = (Student) o;return Objects.equals(name, student.name);}@Overridepublic int hashCode() {return Objects.hash(name);}
}/*** @Description: 迭代器接口* @Date: 2025-01-10 13:43* @Author: gaoyufei**/
public interface Iterator<E> {boolean hasNext();E next();
}import java.util.List;
/*** @Description: 学生迭代器实现* @Date: 2025-01-10 13:44* @Author: gaoyufei**/
public class StudentIterator implements Iterator{private List<Student> students;private int position;public StudentIterator(List<Student> students){this.students=students;this.position=0;}@Overridepublic boolean hasNext() {return position<students.size();}@Overridepublic Object next() {return students.get(position++);}
}import java.util.ArrayList;
import java.util.List;
/*** @Description: 班级* @Date: 2025-01-10 13:47* @Author: gaoyufei**/
public class StudentClass {private List<Student> students=new ArrayList<>();public void add(Student student){this.students.add(student);}public void remove(Student student) {students.remove(student);}public Iterator iterator(){return new StudentIterator(students);}
}/*** @Description: 客户端* @Date: 2025-01-10 13:50* @Author: gaoyufei**/
public class Client {public static void main(String[] args) {StudentClass studentClass=new StudentClass();studentClass.add(new Student("张三"));studentClass.add(new Student("李四"));studentClass.add(new Student("王五"));studentClass.remove(new Student("王五"));Iterator<Student> iterator = studentClass.iterator();while (iterator.hasNext()){System.out.println(iterator.next().getName());}}
}