如何将list集合转换为二维数组？

Question

public List<Schedule> selectSchedule(Integer class_id) {
    List<Schedule> list = new ArrayList<Schedule>();
    Connection connection = null;
    try {
        // 数据库链接
        connection = MysqlConnector.openConnection();
        StringBuffer stringBuffer = new StringBuffer("select * from schedule where 1=1");
        List<Object> paramsList = new ArrayList<Object>();
        if (class_id != null && !"".equals(class_id)) {
            stringBuffer.append(" and class_id=?");// 添加的条件，拼接到SQL语句中
            paramsList.add(class_id);
        }
        PreparedStatement preparedStatement = connection.prepareStatement(stringBuffer.toString());
        for (int i = 1; i <= paramsList.size(); i++) {
            preparedStatement.setObject(i, paramsList.get(i - 1));
        }
        ResultSet resultSet = preparedStatement.executeQuery();
        while (resultSet.next()) {
            Schedule schedule = new Schedule();
            Integer class_id1 = resultSet.getInt("class_id");
            Integer teacher_id = resultSet.getInt("teacher_id");
            String week_days = resultSet.getString("week_days");
            String time_no = resultSet.getString("time_no");
            String curriculum = resultSet.getString("curriculum");
            schedule.setClass_id(class_id1);
            schedule.setTeacher_id(teacher_id);
            schedule.setWeek_days(week_days);
            schedule.setTime_no(time_no);
            schedule.setCurriculum(curriculum);
            list.add(schedule);
            String[][] sch = new String[list.size()][];
            for (int i = 0; i < list.size(); i++) {
                sch[i][0] = list.get(i).getWeek_days();//将星期赋值到数组
                for (int j = 1; j < 5; j++) {
                    sch[i][j]=list.get(i).getCurriculum();//将课程赋值到数组
                }
            }
            for (int i = 0; i < sch[i].length; i++) {//输出数组中的内容
                for (int j = 0; j < sch[j].length; j++) {
                    System.out.println(sch[i][j]);
                }
            }
            /*
             * System.out.println("class_id:" + class_id1 + "week_days:" + week_days +
             * "time_no:" + time_no + "curriculum" + curriculum + "teacher_id:" +
             * teacher_id);
             */
        }
    } catch (SQLException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } finally {
        if (connection != null) {
            try {
                connection.close();
            } catch (Exception e) {
                // TODO: handle exception
                e.printStackTrace();
            }
        }
    }
    return list;
}

画圈的是我写的装换代码

Answer 1

list中包含的是什么类型 是本身就是二维list吗给你一个例子 你参考一下：

package Test;

import java.util.ArrayList;
import java.util.List;

public class T {

    public static void main(String[] args) {
        List list = new ArrayList();
        String[] str1 = { "a", "1" };
        String[] str2 = { "b", "2" };
        String[] str3 = { "c", "3" };
        list.add(str1);
        list.add(str2);
        list.add(str3);

        Object[] s = (Object[]) list.toArray();
        String[][] aa = new String[s.length][];
        for (int i = 0; i < s.length; i++) {
            aa[i] = (String[]) s[i];
        }
        // 输出二维数组的值
        for (int z = 0; z < aa.length; z++) {
            for (int i = 0; i < aa[z].length; i++) {
                System.out.print(aa[z][i] + "\t");
            }
        }

    }

}