需求分析：写一个较为严谨的学生选课系统，实现学生可以选择多门选课课程，并将有效选课结果保存到数据库。

学生需要登录后，才能选课。

让学生可以在选课系统通过多种方式查询到要选的课程信息。

//选课规则：1、每个学生可以选多门课程，多次选课的总学分不能超过6学分；2、不能重复选择一门课程；3、每一门课程的选课人数都有数量限制，当某门课程的选课名额满时，则应另选课程。

4、凭用户名和密码登录，通过提交某一课程号来选课//总体设计方案：建立三个类：登录类register，选课类studentChooseCourse,数据库工具类JDBCUtil；一个SQL脚本文件用于生成数据库表结构和初始记录，以搭建数据库环境。

登录类register类，负责对用户的身份进行验证；工具类JDBCUtil用于实现连接，你可调用JDBCUtil的getConnection()方法等到链接。

选课类studentChooseCourse用于，实现选课功能。

其中包括几个主要方法：1、actionPerformed(ActionEvent) 用于监听用户“查询”和“提交”操作，并负责调用各种方法对其进行处理2、createSearchCourse()用于产生图形用户界面3、processBeforeCommit()用于对用户的“提交”查找进行验证，剔除无效的用户操作4、tryCommit()负责对有效的“提交”操作，进一步处理，并将有效的操作结果时时保存到数据库，并更新数据库原有信息//本程序用到的知识点：数据库连接JDBC；SQL建表、插入输入、动态查询；图形用户界面的产生以及处理查询结果集并较好显示；程序设计基础知识。

//代码如下：import java.awt.GridLayout;import java.awt.event.ActionEvent;import java.awt.event.ActionListener;import java.sql.*;import javax.swing.*;import javax.swing.table.DefaultTableModel;import school.schoolPicture.JdbcUtil;public class StudentChooseCourse extends JFrame implements ActionListener { JTextField jtfSearch = new JTextField(11);String[] columnNames = new String[] { "课程ID", "课程名", "学时", "学分", "学期", "性质" };DefaultTableModel dtmSearch = new DefaultTableModel(columnNames, 27); JTable jtSearch = new JTable(dtmSearch);JScrollPane jspSearch = new JScrollPane(jtSearch);JComboBox jcbSearch = new JComboBox();JTextField jtfSelectedCourse = new JTextField(10);Connection con = null;PreparedStatement ps = null;ResultSet rs = null;private static String usrName;private static String passwrd;public StudentChooseCourse(String usrName, String passwrd) { createSearchCourse();rName = usrName;this.passwrd = passwrd;}public String getUsrName() {return usrName;}public void setUsrName(String usrName) {rName = usrName;}public String getPasswrd() {return passwrd;}public void setPasswrd(String passwrd) {this.passwrd = passwrd;}public void actionPerformed(ActionEvent e) {String str = e.getActionCommand();if ("查询".trim().equals(str)) {int k = 1;while (k < 10) {for (int i = 1; i < 7; i++) {jtSearch.setValueAt(null, k - 1, i - 1);}k++;}searchAvailableCourse();} else if ("提交".equals(str)) {boolean effect=processBeforeCommit();if(effect==true){tryCommit();}}}public boolean processBeforeCommit(){int k = 1;while (k < 10) {for (int i = 1; i < 7; i++) {jtSearch.setValueAt(null, k - 1, i - 1);}k++;}String userInput = jtfSelectedCourse.getText().toString().trim().toLowerCase();String sql = "select cno from coursexx where cno=? ";boolean flagCourseExist = false;try {ps = con.prepareStatement(sql);ps.setString(1, userInput);rs = ps.executeQuery();flagCourseExist = rs.next();} catch (Exception eC) {eC.printStackTrace();}if (!flagCourseExist) {JOptionPane.showMessageDialog(null, "该课程不存在，请重新输入"); return false;}PreparedStatement ps = null;sql = "select sum(grade) "+ "from (select x.sname , o,k.grade grade "+ "from coursexx k join choicesxx x "+ "on o=o and x.sname=?) result";String grade =null;try {ps = con.prepareStatement(sql);ps.setString(1, usrName);rs = ps.executeQuery();while (rs.next()) {grade = rs.getString(1);if(grade==null){grade="0";}}} catch (Exception rrr) {rrr.printStackTrace();}System.out.println("总学分：" + grade);if (Integer.parseInt(grade) > 6) {JOptionPane.showMessageDialog(null, "你已经选满6学分，系统将退出"); this.setVisible(false);return false;}sql = "select * from choicesxx where sname=? and cno=?";boolean flag = false;try {ps = con.prepareStatement(sql);ps.setString(1, this.getUsrName());ps.setString(2, userInput);rs = ps.executeQuery();flag = rs.next();} catch (Exception eaa) {eaa.printStackTrace();}if (flag) {JOptionPane.showMessageDialog(null, "你已经选择了该课程。

请另选课程"); return false;}return true;}public void tryCommit() {String userInput = jtfSelectedCourse.getText().toString().trim().toLowerCase();PreparedStatement ps;String sql = "select (Max-selectedCount) as RemainedCount "+ "from Coursexx where cno=?";try {ps = con.prepareStatement(sql);ps.setString(1, userInput);rs = ps.executeQuery();ResultSetMetaData meta = rs.getMetaData();int cols = meta.getColumnCount();int RemainedCount = -1;while (rs.next()) {RemainedCount = rs.getInt(1);System.out.println("RemainedCount:" + RemainedCount);}if (RemainedCount > 0) {sql = "insert into choicesxx values(?,?)";ps = con.prepareStatement(sql);ps.setString(1, this.getUsrName());ps.setString(2, userInput);ps.executeUpdate();JOptionPane.showMessageDialog(null, "选课成功：" + this.getUsrName()+ " 选了" + userInput + "." + "" + " 还有" + RemainedCount+ " 人可以选该课程。