java课程设计大作业

package Students; import java.util.Scanner; import java.sql.*; public class Main { public static void main(String[] args) { //创建集合对象，用于存储学生数据 //不让程序结束 while (true) { System.out.println("-----欢迎来到学生管理系统-----"); System.out.println("1.增加"); System.out.println("2.打印某班级全部学生"); System.out.println("3.查询"); System.out.println("4.更改"); System.out.println("5.删除学生信息"); System.out.println("6.统计信息: 打印当前在读学生数量"); System.out.println("7.统计信息: 打印某班级学生数量"); System.out.println("请输入你的选择"); Scanner sc = new Scanner(System.in); String choice = sc.nextLine(); switch (choice) { case "1": addStudents(); break; case "2": callPrintStudentsByClass(); break; case "3": callFindStudents(); break; case "4": callupdateStudents(); break; case "5": callDeleteStudent(); break; case "6": callcountAll(); break; case "7": callcountClass(); break; default: System.exit(0); break; } } } public static void callcountClass() { Connection c; Statement stmt; System.out.println("请输入班级号"); Scanner sc = new Scanner(System.in); String classNum = sc.nextLine(); int sum = 0; try { c = connectDataBase(); if (c == null) throw new NullPointerException("Connect failed"); stmt = c.createStatement(); ResultSet rs = stmt.executeQuery("SELECT * FROM Students"); while (rs.next()) { String id = rs.getString("id"); if (id.substring(6, 8).equals(classNum)) { sum++; } } System.out.println("班级号为" + classNum + "的班级中, 学生数量为: " + sum); rs.close(); stmt.close(); c.close(); } catch (Exception e) { System.err.println(e.getClass().getName() + ": " + e.getMessage()); System.out.println("Opened database UNsuccessfully"); } } public static void callcountAll() { Connection c; Statement stmt; int sum = 0; try { c = connectDataBase(); if (c == null) throw new NullPointerException("Connect failed"); stmt = c.createStatement(); ResultSet rs = stmt.executeQuery("SELECT * FROM Students"); while (rs.next()) { sum++; } System.out.println("全校在读学生数量为: " + sum); rs.close(); stmt.close(); c.close(); } catch (Exception e) { System.err.println(e.getClass().getName() + ": " + e.getMessage()); System.out.println("Opened database UNsuccessfully"); } } public static void callDeleteStudent() { Connection c; Statement stmt; System.out.println("请输入需要修改信息的学生学号"); try { Scanner sc = new Scanner(System.in); String ID = sc.nextLine(); c = connectDataBase(); if (c == null) throw new NullPointerException("Connect failed"); stmt = c.createStatement(); ResultSet rs = stmt.executeQuery("SELECT * FROM Students WHERE ID = " + ID); if (rs.next()) { System.out.println("已查询到该学生, 请输入1以确定删除信息"); Scanner sc1 = new Scanner(System.in); String confirm = sc1.nextLine(); if (confirm.equals("1")) { String query = "DELETE FROM Students WHERE ID = ?"; PreparedStatement preparedStmt = c.prepareStatement(query); preparedStmt.setString(1, ID); preparedStmt.executeUpdate(); c.close(); System.out.println("删除学生信息成功！"); return; } else { System.out.println("已取消删除操作"); return; } } else { System.out.println("查无此人"); } rs.close(); stmt.close(); c.close(); } catch (Exception e) { System.err.println(e.getClass().getName() + ": " + e.getMessage()); System.out.println("Opened database UNsuccessfully"); return; } System.out.println("删除成功"); } public static void callupdateStudents() { Connection c; Statement stmt; System.out.println("请输入需要修改信息的学生学号"); try { Scanner sc = new Scanner(System.in); String ID = sc.nextLine(); c = connectDataBase(); if (c == null) throw new NullPointerException("Connect failed"); stmt = c.createStatement(); ResultSet rs = stmt.executeQuery("SELECT * FROM Students WHERE ID = " + ID); if (rs.next()) { System.out.println("请输入需要修改后的学生姓名"); Scanner sc2 = new Scanner(System.in); String newName = sc2.nextLine(); System.out.println("请输入需要修改后的学生学院"); Scanner sc3 = new Scanner(System.in); String newSchool = sc3.nextLine(); System.out.println("请输入需要修改后的学生性别"); Scanner sc4 = new Scanner(System.in); String newSex = sc4.nextLine(); String query = "UPDATE Students SET NAME = ?, SCHOOL = ?,SEX=? WHERE ID = ?"; PreparedStatement preparedStmt = c.prepareStatement(query); preparedStmt.setString(1, newName); preparedStmt.setString(2, newSchool); preparedStmt.setString(3, newSex); preparedStmt.setString(4, ID); // execute the java preparedstatement preparedStmt.executeUpdate(); c.close(); System.out.println("更新学生信息成功！"); } else { System.out.println("查无此人"); } rs.close(); stmt.close(); c.close(); } catch (Exception e) { System.err.println(e.getClass().getName() + ": " + e.getMessage()); System.out.println("Opened database UNsuccessfully"); return; } System.out.println("更改成功"); } public static void callPrintStudentsByClass() { Connection c; Statement stmt; System.out.println("请输入班级号"); Scanner sc = new Scanner(System.in); String classNum = sc.nextLine(); try { c = connectDataBase(); if (c == null) throw new NullPointerException("Connect failed"); stmt = c.createStatement(); ResultSet rs = stmt.executeQuery("SELECT * FROM Students"); while (rs.next()) { String id = rs.getString("id"); String name = rs.getString("name"); String school = rs.getString("school"); String sex = rs.getString("sex");