17、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

【例】定义一个可以存储学生对象的容器对象，将遍历该容器的功能交由迭代器实现，涉及到的类如
下：

public class Student {
    public Student(String name, String number) {
        this.name = name;
        this.number = number;
    }

    private String name;
    private String number;

    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", 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;
    }
}

//抽象迭代器角色接口
public interface StudentIterator {
    //判断是否还有元素
    boolean hasNext();
    //获取下一个元素
    Student next();
}

//具体迭代器类
public class StudentIteratorImpl implements StudentIterator {
    private List<Student> list;
    //用来记录遍历时的位置
    private int position=0;

    public StudentIteratorImpl(List<Student> list) {
        this.list = list;
    }

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

    @Override
    public Student next() {
        //从集合中获取指定位置的元素
        Student currentStudent = list.get(position);
        position++;
        return currentStudent;
    }
}

//抽象聚合角色接口
public interface StudentAggregate {
    //添加学生功能
    void addStudent(Student stu);
    //删除学生功能
    void removeStudent(Student stu);
    //获取迭代器对象功能
    StudentIterator getStudentIterator();
}

//具体聚合（ConcreteAggregate）角色
public class StudentAggregateImpl implements StudentAggregate {
    private List<Student> list=new ArrayList<>();
    @Override
    public void addStudent(Student stu) {
        list.add(stu);
    }

    @Override
    public void removeStudent(Student stu) {
        list.remove(stu);
    }

    @Override
    public StudentIterator getStudentIterator() {
        return new StudentIteratorImpl(list);
    }
}

public class Client {
    public static void main(String[] args) {
        //创建聚合对象
        StudentAggregateImpl aggregate=new StudentAggregateImpl();
        //添加元素
        aggregate.addStudent(new Student("张三","001"));
        aggregate.addStudent(new Student("李四","002"));
        aggregate.addStudent(new Student("王五","003"));
        aggregate.addStudent(new Student("赵六","004"));
        //遍历聚合对象

        //1,获取迭代器对象
        StudentIterator iterator = aggregate.getStudentIterator();
        //2,遍历
        while (iterator.hasNext()){
            Student student = iterator.next();
            System.out.println(student);
        }
    }
}