1 概念
迭代器模式在设计模式中属于行为型模式，用于顺序访问集合对象的元素，不需要知道集合对象的底层表示。
迭代器模式的结构中包括四种角色：
- 抽象集合（Abstract Aggregate）
- 具体集合（Concrete Aggregate）
- 抽象迭代器（Abstract Iterator）
- 具体迭代器（Concrete Iterator）
2 案例说明
对Student类实现迭代输出
网络异常，图片无法展示
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3 代码实现
Aggregate.java
/** * @desc: 集合容器抽象 * @author: YanMingXin * @create: 2021/8/31-15:53 **/ public interface Aggregate { public Iterator iterator(); } 复制代码
Iterator.java
/** * @desc: 抽象迭代器 * @author: YanMingXin * @create: 2021/8/31-15:53 **/ public interface Iterator<E> { public boolean hasNext(); public E next(); } 复制代码
Student.java
/** * @desc: Student实体类 * @author: YanMingXin * @create: 2021/8/31-15:54 **/ public class Student { private Integer id; private String name; private Integer age; public Student() { } public Student(Integer id, String name, Integer age) { this.id = id; this.name = name; this.age = age; } public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public Integer getAge() { return age; } public void setAge(Integer age) { this.age = age; } @Override public String toString() { return "Student{" + "id=" + id + ", name='" + name + '\'' + ", age=" + age + '}'; } } 复制代码
StudentIterator.java
/** * @desc: 具体迭代器 * @author: YanMingXin * @create: 2021/8/31-15:55 **/ public class StudentIterator implements Iterator { private StudentShelf studentShelf; private int index; public StudentIterator(StudentShelf studentShelf) { this.studentShelf = studentShelf; this.index = 0; } @Override public boolean hasNext() { if (index < studentShelf.getLength()) { return true; } return false; } @Override public Object next() { Student studentAt = studentShelf.getStudentAt(index); index += 1; return studentAt; } } 复制代码
StudentShelf.java
/** * @desc: 集合容器具体实现 * @author: YanMingXin * @create: 2021/8/31-16:11 **/ public class StudentShelf implements Aggregate { private Student[] students; private int size = 0; private final int DEFAULT_SIZE = 10; public StudentShelf() { this.students = new Student[DEFAULT_SIZE]; } public StudentShelf(int maxsize) { this.students = new Student[maxsize]; } public Student getStudentAt(int index) { return students[index]; } public void appendStudent(Student student) { this.students[size] = student; size++; if (size >= DEFAULT_SIZE) { //扩容 Student[] stus = new Student[size * 2]; System.arraycopy(this.students, 0, stus, 0, this.students.length); this.students = stus; } } public int getLength() { return size; } @Override public Iterator<Student> iterator() { return new StudentIterator(this); } } 复制代码
MyIterator.java
/** * @desc: 迭代器模式测试 * @author: YanMingXin * @create: 2021/8/31-15:51 **/ public class MyIterator { public static void main(String[] args) { StudentShelf shelf = new StudentShelf(); shelf.appendStudent(new Student(1,"zs",23)); shelf.appendStudent(new Student(2,"ls",24)); shelf.appendStudent(new Student(3,"ww",25)); Iterator<Student> iterator = shelf.iterator(); while (iterator.hasNext()){ Student next = iterator.next(); System.out.println(next); } } } 复制代码
测试结果：
网络异常，图片无法展示
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4 小总结
迭代器模式相比其他设计模式感觉实现起来麻烦一些，而且还不如for循环好用，那是因为Java内部已经集成了迭代器模式，这样就不用我们开发人员每次使用都进行迭代，而可以直接使用。
