一、介绍

1、迭代器模式（Iterator Pattern）是常用的设计模式，属于行为模式。

2、如果集合元素是不同的方式实现的，有数组，还有java的集合类，或者还有其他的方式，当客户端要遍历这些集合元素 => 可以考虑迭代器模式。

3、迭代器模式：提供一种遍历集合元素的统一接口，用一致的方法遍历集合元素，不需要知道集合对象的底层表示，不暴漏其内部的结构。

1）Iterator：迭代器接口，系统提供。含义hasNext,next ,remove

2）ConcreteIterator:具体的迭代器类，管理迭代

3）Aggregate:一个统一的聚合接口，将客户端和具体聚合解耦

4）ConcreteAggregate:具体的聚合持有对象集合，并提供一个方法，返回一个迭代器，该迭代器可以正确遍历集合

5）Client:客户端 通过Iterator和Aggregate依赖子类

二、代码

package com.hao.demo.design.ietrator;import java.util.Iterator;/*** @author* @date 2020-05-25*/
public interface College {String getName();// 增加系的方法void addDepartment(String name, String desc);// 返回一个迭代器，遍历public Iterator createIterator();
}package com.hao.demo.design.ietrator;import java.util.Iterator;/*** @author haojunhu* @date 2020-05-25*/
public class ComputerCollege implements College {Department[] departments;int numOfDepartment = 0; // 保存当前数组的对象个数public ComputerCollege() {departments = new Department[5];addDepartment("java", "java专业");addDepartment("php", "php");addDepartment("python", "python");addDepartment("js", "js");}@Overridepublic String getName() {return "计算机学院";}@Overridepublic void addDepartment(String name, String desc) {Department department = new Department(name, desc);departments[numOfDepartment] = department;numOfDepartment += 1;}// 返回迭代器@Overridepublic Iterator createIterator() {return new ComputerCollegeIterator(departments);}
}package com.hao.demo.design.ietrator;import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;/*** @author* @date 2020-05-25*/
public class InfoColleage implements College {List<Department> departments;public InfoColleage() {departments = new ArrayList<>();addDepartment("信息安全", "信息安全");addDepartment("网络安全", "网络安全");}@Overridepublic String getName() {return "信息工程系";}@Overridepublic void addDepartment(String name, String desc) {Department department = new Department(name, desc);departments.add(department);}@Overridepublic Iterator createIterator() {return new InfoColleageIterator(departments);}
}package com.hao.demo.design.ietrator;import java.util.Iterator;/*** @author* @date 2020-05-25*/
public class ComputerCollegeIterator implements Iterator {// 这里需要知道Department 是以什么方式存储Department[] departments;int position = 0; // 遍历的位置public ComputerCollegeIterator(Department[] departments) {this.departments = departments;}/*** 判断是否含有下一个元素** @return*/@Overridepublic boolean hasNext() {if (position >= departments.length || departments[position] == null) {return false;} else {return true;}}/*** @return*/@Overridepublic Object next() {Department department = departments[position];position += 1;return department;}// 删除方法没实现public void remove() {}
}package com.hao.demo.design.ietrator;import java.util.Iterator;
import java.util.List;/*** @author* @date 2020-05-25*/
public class InfoColleageIterator implements Iterator {List<Department> departments; // 信息工程学院是以List方式存放int index = -1; // 索引public InfoColleageIterator(List<Department> departments) {this.departments = departments;}@Overridepublic boolean hasNext() {if (index >= departments.size() - 1) {return false;} else {index += 1;return true;}}@Overridepublic Object next() {return departments.get(index);}// 删除方法没实现public void remove() {}
}package com.hao.demo.design.ietrator;import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;/*** @author* @date 2020-05-25*/
@Data
@AllArgsConstructor
@NoArgsConstructor
public class Department {private String name;private String desc;
}package com.hao.demo.design.ietrator;import java.util.Iterator;
import java.util.List;/*** @author* @date 2020-05-25*/
public class OutPutImpl {// 拿到学院集合List<College> colleges;public OutPutImpl(List<College> colleges) {this.colleges = colleges;}//public void printCollege() {// 从colleges 取出所以学院 java list 实现了IteratorIterator<College> iterator = colleges.iterator();while (iterator.hasNext()) {// 取出一个学院College college = iterator.next();System.out.println("===学院名称====");printDepartment(college.createIterator()); // 得到对应的迭代器}}// 输出 学院输出系public void printDepartment(Iterator iterator) {while (iterator.hasNext()) {Department department = (Department) iterator.next();System.out.println(department.getName());}}}package com.hao.demo.design.ietrator;import java.util.ArrayList;/*** @author* @date 2020-05-25*/
public class Client {public static void main(String[] args) {// 创建学院ArrayList<College> colleges = new ArrayList<>();ComputerCollege computerCollege = new ComputerCollege();InfoColleage infoColleage = new InfoColleage();colleges.add(computerCollege);colleges.add(infoColleage);OutPutImpl outPut = new OutPutImpl(colleges);outPut.printCollege();}
}