迭代器模式

1.定义：提供一种方法，顺序访问一个集合对象中的各个元素，而又不暴露该对象的内部表示。

2.类型：行为型

3.适用场景：访问一个集合对象的内容而无需暴露它的内部表示；
　　　　　   为遍历不同的集合结构提供一个统一的接口。

4.优点：分离了集合对象的遍历行为。

5.缺点：类的个数成对增加。

6.相关设计模式：访问者模式。

7.实例目录package

8.实例UML类图

9.代码

package com.geely.design.pattern.behavioral.iterator;

public class Course {
    private String name;

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

    public String getName(){
        return name;
    }
}

package com.geely.design.pattern.behavioral.iterator;

public interface CourseIterator {
    Course nextCourse();
    boolean isLastCourse();
}

package com.geely.design.pattern.behavioral.iterator;

import java.util.List;

public class CourseIteratorImpl implements CourseIterator {

    private List<Course> courseList;
    private int position;
    private Course course;

    public CourseIteratorImpl(List<Course> courseList) {
        this.courseList = courseList;
    }

    @Override
    public Course nextCourse() {
        System.out.println("返回课程，位置是：" + position);
        course = courseList.get(position);
        position++;
        return course;
    }

    @Override
    public boolean isLastCourse() {
        if(position < courseList.size()){
            return false;
        }
        return true;
    }
}

package com.geely.design.pattern.behavioral.iterator;

public interface CourseAggregate {
    void addCourse(Course course);
    void removeCourse(Course course);
    CourseIterator getCourseIterator();
}

package com.geely.design.pattern.behavioral.iterator;

import java.util.ArrayList;
import java.util.List;

public class CourseAggregateImpl implements CourseAggregate {
    private List<Course> courseList;

    public CourseAggregateImpl() {
        this.courseList = new ArrayList<>();
    }

    @Override
    public void addCourse(Course course) {
        courseList.add(course);
    }

    @Override
    public void removeCourse(Course course) {
        courseList.remove(course);
    }

    @Override
    public CourseIterator getCourseIterator() {
        return new CourseIteratorImpl(courseList);
    }
}

package com.geely.design.pattern.behavioral.iterator;

public class Test {
    public static void main(String[] args) {
        Course course1 = new Course("Java电商一期");
        Course course2 = new Course("Java电商二期");
        Course course3 = new Course("Java设计模式精讲");
        Course course4 = new Course("Python课程");
        Course course5 = new Course("算法课程");
        Course course6 = new Course("前端课程");

        CourseAggregate courseAggregate = new CourseAggregateImpl();
        courseAggregate.addCourse(course1);
        courseAggregate.addCourse(course2);
        courseAggregate.addCourse(course3);
        courseAggregate.addCourse(course4);
        courseAggregate.addCourse(course5);
        courseAggregate.addCourse(course6);
        
        System.out.println("------------课程列表--------------");
        printCourses(courseAggregate);

        courseAggregate.removeCourse(course4);
        courseAggregate.removeCourse(course5);

        System.out.println("------------删除操作之后的课程列表--------------");
        printCourses(courseAggregate);
    }

    private static void printCourses(CourseAggregate courseAggregate) {
        CourseIterator courseIterator = courseAggregate.getCourseIterator();
        while(!courseIterator.isLastCourse()){
            Course course = courseIterator.nextCourse();
            System.out.println(course.getName());
        }
    }
}