Java设计模式之迭代器模式

定义

提供一个对象来顺序访问聚合对象中的一系列数据，而不暴露聚合对象的内部表示。

结构

迭代器模式主要包含以下角色：

抽象聚合角色：定义存储、添加、删除聚合元素以及创建迭代器对象的接口。
具体聚合角色：实现抽象聚合类，返回一个具体迭代器的实例。
抽象迭代器角色：定义访问和遍历聚合元素的接口，通常包含 hasNext()、next() 等方法。
具体迭代器角色：实现抽象迭代器接口中所定义的方法，完成对聚合对象的遍历，记录遍历的当前位置。

案例

抽象聚合类

public interface StudentAggregate {//添加元素void addStudent(Student student);//删除元素void deleteStudent(Student student);//创建迭代器对象ConcreteIterator getIterator();
}

具体聚合类

public class ConcreteAggregate implements StudentAggregate{private List<Student> list =new ArrayList<>();@Overridepublic void addStudent(Student student) {list.add(student);}@Overridepublic void deleteStudent(Student student) {list.remove(student);}@Overridepublic ConcreteIterator getIterator() {return new ConcreteIterator(list);}
}

抽象迭代器

public interface StudentIterator {boolean hasNext();Student next();
}

具体迭代器类

public class ConcreteIterator implements StudentIterator {private List<Student> list = new ArrayList<>();private int index = 0;public ConcreteIterator(List<Student> list) {this.list = list;}@Overridepublic boolean hasNext() {return index < list.size();}@Overridepublic Student next() {Student student = list.get(index);index++;return student;}
}

载体

public class Student {private String name;private String Id;public Student(String name, String id) {this.name = name;Id = id;}@Overridepublic String toString() {return "Student{" +"name='" + name + '\'' +", Id='" + Id + '\'' +'}';}
}

测试

public class Client {public static void main(String[] args) {ConcreteAggregate concreteAggregate = new ConcreteAggregate();concreteAggregate.addStudent(new Student("张三","NO1"));concreteAggregate.addStudent(new Student("李四","NO2"));concreteAggregate.addStudent(new Student("王五","NO3"));ConcreteIterator iterator = concreteAggregate.getIterator();while(iterator.hasNext()){Student currentStudent = iterator.next();System.out.println(currentStudent.toString());}}
}