使用 Java 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 data = new ArrayList();

        try {
            PreparedStatement ps = connection.prepareStatement(
                    "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 = ?");
            ps.setInt(1, id_user); // 使用参数化查询，防止 SQL 注入
            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;
    }

    // 辅助方法：根据 id 获取关注者姓名 (需要根据实际情况修改)
    private String getFollowerName(int id_follower) {
        String followerName = "Unknown";
        try {
            PreparedStatement ps = connection.prepareStatement("SELECT name FROM users WHERE id = ?");
            ps.setInt(1, id_follower);
            ResultSet rs = ps.executeQuery();
            if (rs.next()) {
                followerName = rs.getString("name");
            }
            rs.close();
            ps.close();
        } catch (SQLException e) {
            e.printStackTrace();
            JOptionPane.showMessageDialog(null, "getFollowerName():" + e.getMessage());
        }
        return followerName;
    }

    // 示例用法 (需要根据实际情况修改)
    public static void main(String[] args) {
        // 假设已经建立了数据库连接
        Connection connection = null; // 替换为你的数据库连接代码
        SocialNetwork socialNetwork = new SocialNetwork(connection);
        ArrayList mutualFollowers = socialNetwork.listMutualFollowers(123); // 假设用户ID为 123

        if (mutualFollowers != null) {
            System.out.println("Mutual Followers:");
            for (Object[] follower : (ArrayList<Object[]>) mutualFollowers) {
                System.out.println(follower[0]);
            }
        } else {
            System.out.println("Failed to retrieve mutual followers.");
        }
    }
}