public interface Collection<E> extends Iterable<E> {}

public interface Iterable<T> {
    Iterator<T> iterator();
}

List<String> list = Arrays.asList("A", "B", "C");
Iterator<String> iterator = list.iterator();
while (iterator.hasNext()) {
    System.out.println(iterator.next());
}

// 自定義集合
class MyCollection implements Iterable<Integer> {
    private List<Integer> data = new ArrayList<>();

    public void add(int value) {
        data.add(value);
    }

    @Override
    public Iterator<Integer> iterator() {
        return new MyIterator();
    }

    // 自定義迭代器
    private class MyIterator implements Iterator<Integer> {
        private int index = 0;

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

        @Override
        public Integer next() {
            return data.get(index++);
        }
    }
}

/**
 * @author Created by njy on 2023/6/25
 * 學生實體類
 */
@Data
public class Student {
    private String name;
    private Integer age;
    public Student(String name,Integer age){
        this.age=age;
        this.name=name;
    }
}

import java.util.Iterator;
/**
 * @author Created by njy on 2023/6/25
 * 抽象迭代器（Iterator）：學生迭代器
 * 實現(xiàn)Iterator接口
 * 負責定義訪問和遍歷元素的接口，例如提供hasNext()和next()方法。
 */
public interface StudentIterator extends Iterator<Student> {
}

/**
 * @author Created by njy on 2023/6/25
 * 具體迭代器（Concrete iterator）：
 * 實現(xiàn)抽象迭代器定義的接口，負責實現(xiàn)對元素的訪問和遍歷。
 */
public class StudentListIterator implements StudentIterator{
    private List<Student> students;
    private int index;
 
    public StudentListIterator(List<Student> students) {
        this.students = students;
        this.index = 0;
    }
 
    //檢查是否還有下一個元素
    @Override
    public boolean hasNext() {
        return (index < students.size());
    }
 
    //返回下一個元素
    @Override
    public Student next() {
        if (!hasNext()) {
            throw new NoSuchElementException();
        }
        Student student = students.get(index);
        index++;
        return student;
    }
}

/**
 * @author Created by njy on 2023/6/25
 * 抽象聚合器（Aggregate）：學生聚合器
 * 提供創(chuàng)建迭代器的接口，例如可以定義一個iterator()方法。
 */
public interface StudentAggregate {
    //用于創(chuàng)建具體的迭代器對象
    StudentIterator iterator();
    void add(Student student);
}

/**
 * @author Created by njy on 2023/6/25
 * 具體聚合器（ConcreteAggregate）：班級列表
 * 實現(xiàn)抽象聚合器定義的接口，負責創(chuàng)建具體的迭代器對象，并返回該對象。
 */
public class ClassList implements StudentAggregate{
    private List<Student> students = new ArrayList<>();
 
    //創(chuàng)建迭代器對象
    @Override
    public StudentIterator iterator() {
        return new StudentListIterator(students);
    }
 
    //向班級名單中添加學生信息
    @Override
    public void add(Student student) {
        students.add(student);
    }
}

/**
 * @author Created by njy on 2023/6/25
 * 迭代器模式測試類
 */
@SpringBootTest
public class TestIterator {
    @Test
    void testIterator(){
        ClassList classList = new ClassList();
        // 添加學生信息
        classList.add(new Student("張三", 18));
        classList.add(new Student("李四", 19));
        classList.add(new Student("王五", 20));
        // 獲取迭代器，遍歷學生信息
        StudentIterator iterator = classList.iterator();
        while(iterator.hasNext()) {
            Student student = iterator.next();
            System.out.println("學生姓名：" + student.getName() + "，學生年齡：" + student.getAge());
        }
    }
 
}

輸出：
學生姓名：張三，學生年齡：18
學生姓名：李四，學生年齡：19
學生姓名：王五，學生年齡：20

import java.util.*;

public class CollectionIteratorExample {
    public static void main(String[] args) {
        List<String> list = Arrays.asList("A", "B", "C");
        Iterator<String> iterator = list.iterator();

        while (iterator.hasNext()) {
            System.out.println(iterator.next());
        }
    }
}

import java.sql.*;
import java.util.Iterator;

public class JdbcIteratorExample {
    public static void main(String[] args) {
        String url = "jdbc:mysql://localhost:3306/mydb";
        String user = "root";
        String password = "password";

        try (Connection conn = DriverManager.getConnection(url, user, password);
             Statement stmt = conn.createStatement();
             ResultSet rs = stmt.executeQuery("SELECT id, name FROM users")) {

            // 使用自定義迭代器遍歷 ResultSet
            Iterator<User> userIterator = new ResultSetIterator<>(rs);
            while (userIterator.hasNext()) {
                User user = userIterator.next();
                System.out.println(user);
            }

        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    // 自定義迭代器
    static class ResultSetIterator<T> implements Iterator<T> {
        private final ResultSet rs;
        private final RowMapper<T> rowMapper;

        public ResultSetIterator(ResultSet rs) throws SQLException {
            this.rs = rs;
            this.rowMapper = (rs1) -> {
                User user = new User();
                user.setId(rs1.getInt("id"));
                user.setName(rs1.getString("name"));
                return user;
            };
        }

        @Override
        public boolean hasNext() throws SQLException {
            return rs.next();
        }

        @Override
        public T next() throws SQLException {
            return rowMapper.mapRow(rs);
        }
    }

    // 輔助類
    static class User {
        private int id;
        private String name;

        // Getters and setters
        @Override
        public String toString() {
            return "User{" + "id=" + id + ", name='" + name + '\'' + '}';
        }
    }

    interface RowMapper<T> {
        T mapRow(ResultSet rs) throws SQLException;
    }
}