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<>();

    @Override
    public void addStudent(Student student) {
        list.add(student);
    }

    @Override
    public void deleteStudent(Student student) {
        list.remove(student);
    }

    @Override
    public 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;
    }

    @Override
    public boolean hasNext() {
        return index < list.size();
    }

    @Override
    public 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;
    }

    @Override
    public 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());
        }
    }
}