Connection con = DBconn.getConnection();

DBconn就是仿照的連接數據庫類

可是我定義了一個新的類，同時類有靜態方法 為什么不可以這么用了？

userDao類：

package dao;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.ArrayList;

import Data.DBconn;
import entity.user;

public class userDao {
?? ?public userDao(){};
?? ?// 將所有user放到ArrayList中
?? ?public ArrayList<user> getAllUsers() {
?? ??? ?Connection conn = null;// 初始定義
?? ??? ?PreparedStatement stmt = null;// 初始定義
?? ??? ?ResultSet rs = null;// 初始定義
?? ??? ?ArrayList<user> list = new ArrayList<user>();// 初始聲明
?? ??? ?try {
?? ??? ??? ?conn = DBconn.getConnection();// 建立連接
?? ??? ??? ?String sql = "select * from user";// sql語句
?? ??? ??? ?stmt = conn.prepareStatement(sql);
?? ??? ??? ?rs = stmt.executeQuery();
?? ??? ??? ?while (rs.next()) {

?? ??? ??? ???? user us = new user();
?? ??? ??? ??? ?us.setId(rs.getInt("id"));
?? ??? ??? ??? ?us.setUsertel(rs.getString("usertel"));
?? ??? ??? ??? ?us.setUseremail(rs.getString("useremail"));
?? ??? ??? ??? ?us.setPassword(rs.getString("password"));
?? ??? ??? ??? ?us.setName(rs.getString("name"));
?? ??? ??? ??? ?us.setGrade(rs.getInt("grade"));
?? ??? ??? ??? ?us.setCards(rs.getString("cards"));
?? ??? ??? ??? ?us.setSign(rs.getString("sign"));
?? ??? ??? ??? ?us.setPer_imag(rs.getString("per_imag"));
?? ??? ??? ??? ?us.setExp(rs.getInt("exp"));
?? ??? ??? ??? ?us.setWarn(rs.getInt("warn"));
?? ??? ??? ??? ?us.setAble(rs.getInt("able"));
?? ??? ??? ??? ?list.add(us);
?? ??? ??? ?}
?? ??? ??? ?return list;// return 執行在finally之后...所以，finally 照樣執行
?? ??? ?} catch (Exception e) {
?? ??? ??? ?e.printStackTrace();
?? ??? ??? ?return null;
?? ??? ?} finally {
?? ??? ??? ?// 釋放 rs stmt ，并且conn不能釋放，因為定義了一個靜態的常量的conn,要給其他需要的地方使用
?? ??? ??? ?if (rs != null) {
?? ??? ??? ??? ?try {
?? ??? ??? ??? ??? ?rs.close();
?? ??? ??? ??? ??? ?rs = null;
?? ??? ??? ??? ?} catch (Exception e) {
?? ??? ??? ??? ??? ?e.printStackTrace();
?? ??? ??? ??? ?}
?? ??? ??? ?}
?? ??? ??? ?if (stmt != null) {
?? ??? ??? ??? ?try {
?? ??? ??? ??? ??? ?stmt.close();
?? ??? ??? ??? ??? ?stmt = null;
?? ??? ??? ??? ?} catch (Exception e) {
?? ??? ??? ??? ??? ?e.printStackTrace();
?? ??? ??? ??? ?}
?? ??? ??? ?}
?? ??? ?}

?? ?}
?? ?public static String getText(){
?? ??? ?return "sss";
?? ?}
}