6.8 迭代器模式

6.8.1 概述

定義：提供一個對象來順序訪問聚合對象中的一系列數據，而不暴露聚合對象的內部表示。

6.8.2 結構

迭代器模式主要包含以下角色：

• 抽象聚合（Aggregate）角色：定義存儲、添加、刪除聚合元素以及創建迭代器對象的接口。
• 具體聚合（ConcreteAggregate）角色：實現抽象聚合類，返回一個具體迭代器的實例。
• 抽象迭代器（Iterator）角色：定義訪問和遍歷聚合元素的接口，通常包含 hasNext()、next() 等方法。
• 具體迭代器（Concretelterator）角色：實現抽象迭代器接口中所定義的方法，完成對聚合對象的遍歷，記錄遍歷的當前位置。

6.8.3 案例實現

【例】定義一個可以存儲學生對象的容器對象，將遍歷該容器的功能交由迭代器實現，涉及到的類如下：

代碼如下：

定義迭代器接口，聲明hasNext、next方法

class Student {private String name;private String number;public Student(String name, String number) {this.name = name;this.number = number;}public String getName() {return name;}public void setName(String name) {this.name = name;}public String getNumber() {return number;}public void setNumber(String number) {this.number = number;}@Overridepublic String toString() {return "Student{" +"name='" + name + '\'' +", number='" + number + '\'' +'}';}
}
//抽象迭代器角色接口
interface StudentIterator {boolean hasNext();Student next();
}
//具體迭代器角色類
class StudentIteratorImpl implements StudentIterator {private List<Student> list;private int position = 0;public StudentIteratorImpl(List<Student> list) {this.list = list;}@Overridepublic boolean hasNext() {return position < list.size();}@Overridepublic Student next() {Student currentStudent = list.get(position);position++;return currentStudent;}
}
interface StudentAggregate {void addStudent(Student student);void removeStudent(Student student);StudentIterator getStudentIterator();
}
class StudentAggregateImpl implements StudentAggregate {private List<Student> list = new ArrayList<Student>();  // 學生列表@Overridepublic void addStudent(Student student) {this.list.add(student);}@Overridepublic void removeStudent(Student student) {this.list.remove(student);}@Overridepublic StudentIterator getStudentIterator() {return new StudentIteratorImpl(list);}
}
class Client{public static void main(String[] args) {//創建聚合對象StudentAggregateImpl studentAggregate = new StudentAggregateImpl();//添加元素studentAggregate.addStudent(new Student("張三","1001001"));studentAggregate.addStudent(new Student("李四","1001002"));studentAggregate.addStudent(new Student("王二","1001003"));studentAggregate.addStudent(new Student("麻子","1001004"));//遍歷聚合對象StudentIterator studentIterator = studentAggregate.getStudentIterator();while(studentIterator.hasNext()){Student student = studentIterator.next();System.out.println(student.toString());}}
}

Student{name='張三', number='1001001'}
Student{name='李四', numbe