Java中如何使用ArrayList列出用户的共同关注者

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import javax.swing.JOptionPane;

public class SocialNetwork {

    private Connection connection; // 假设已建立数据库连接

    public SocialNetwork(Connection connection) {
        this.connection = connection;
    }

    public ArrayList listMutualFollowers(int id_user) {
        ArrayList<Object[]> data = new ArrayList<>();

        try {
            String sql = "SELECT id_follower FROM followers a WHERE id_follower IN (SELECT id_follower FROM followers b WHERE a.id_user = b.id_user) and id_user = ?";
            PreparedStatement ps = connection.prepareStatement(sql);
            ps.setInt(1, id_user);
            ResultSet rs = ps.executeQuery();

            while (rs.next()) {
                data.add(new Object[]{
                    getFollowerName(rs.getInt("id_follower"))
                });
            }

            rs.close();
            ps.close();

        } catch (SQLException e) {
            e.printStackTrace();
            JOptionPane.showMessageDialog(null, "listMutualFollowers():" + e.getMessage());
            return null;
        }

        return data;
    }

    // 假设存在一个方法，根据用户ID获取用户名
    private String getFollowerName(int id_follower) {
        // 实现从数据库或其他数据源获取用户名的逻辑
        // 这里只是一个示例，实际实现需要根据你的数据结构进行调整
        String followerName = "User_" + id_follower; // 示例用户名
        return followerName;
    }
}

// 假设已经创建了 SocialNetwork 对象
SocialNetwork socialNetwork = new SocialNetwork(connection);
int userId = 123; // 替换为实际的用户ID
ArrayList mutualFollowers = socialNetwork.listMutualFollowers(userId);

if (mutualFollowers != null) {
    System.out.println("Mutual followers of user " + userId + ":");
    for (Object[] follower : (ArrayList<Object[]>)mutualFollowers) {
        System.out.println(follower[0]); // 假设用户姓名在Object数组的第一个位置
    }
} else {
    System.out.println("Failed to retrieve mutual followers.");
}