import java.util.ArrayList;
import java.util.Scanner;

/*
    学生管理系统
 */
public class studentManager {
    public static void main(String[] args) {
        ArrayList<student> array = new ArrayList<student>();
        while (true) {
            //用输出语句完成主界面编写
            System.out.println("——————欢迎来到学生管理系统——————");
            System.out.println("1 添加学生");
            System.out.println("2 删除学生");
            System.out.println("3 修改学生");
            System.out.println("4 查看所有学生");
            System.out.println("5 退出系统");
            System.out.println("请输入你的选择：");
            Scanner sc = new Scanner(System.in);
            String line = sc.nextLine();
            switch (line) {
                case "1":
                    //System.out.println("添加学生");
                    addstudent(array);
                    break;
                case "2":
                    //System.out.println("删除学生");
                    deletestudent(array);
                    break;
                case "3":
                    //System.out.println("修改学生");
                    updatestudent(array);
                    break;
                case "4":
                    //System.out.println("查看所有学生");
                    findAllstudent(array);
                    break;
                case "5":
                    System.out.println("谢谢使用！");
                    System.exit(0);//JVM退出
            }
        }
    }

    //定义方法，用于添加学生信息
    public static void addstudent(ArrayList<student> array) {
        //键盘录入学生对象所需要的信息，显示提示信息，提示要输入何种信息
        Scanner sc = new Scanner(System.in);

        String sid;
        while (true) {
            System.out.println("请输入学生学号：");
            sid = sc.nextLine();
            boolean flag = isUsed(array, sid);
            if (flag) {
                System.out.println("你输入的学号已经被使用，请重新输入！");
            } else {
                break;
            }
        }
        System.out.println("请输入学生姓名：");
        String name = sc.nextLine();
        System.out.println("请输入学生年龄：");
        String age = sc.nextLine();
        System.out.println("请输入学生居住地：");
        String address = sc.nextLine();

        //创建学生对象，把键盘录入的数据赋值给学生对象的成员变量
        student s = new student();
        s.setSid(sid);
        s.setName(name);
        s.setAge(age);
        s.setAddress(address);

        //将学生对象添加到集合中
        array.add(s);

        //给出添加成功提示
        System.out.println("添加学生成功！");
    }

    //定义方法，用于查看所有学生信息
    public static void findAllstudent(ArrayList<student> array) {
        if (array.size() == 0) {
            System.out.println("无信息，请先添加信息后再查询");
            return;
        }
        System.out.println("学号\t\t\t姓名\t\t年龄\t\t居住地");

        for (int i = 0; i < array.size(); i++) {
            student s = array.get(i);
            System.out.println(s.getSid() + "\t" + s.getName() + "\t" + s.getAge() + "岁\t" + s.getAddress());
        }
    }

    //定义方法，用于删除学生信息
    public static void deletestudent(ArrayList<student> array) {
        Scanner sc = new Scanner(System.in);
        System.out.println("请输入你要删除的学生的学号：");
        String sid = sc.nextLine();

        int index = -1;
        for (int i = 0; i < array.size(); i++) {
            student s = array.get(i);
            if (s.getSid().equals(sid)) {
                index = i;
                break;
            }
        }
        if (index == -1) {
            System.out.println("该学生信息不存在，请重新输入");
        } else {
            array.remove(index);
            System.out.println("删除学生成功！");
        }
    }

    //定义方法，用于修改学生信息
    public static void updatestudent(ArrayList<student> array) {
        Scanner sc = new Scanner(System.in);
        System.out.println("请输入你要修改的学生的学号：");
        String sid = sc.nextLine();

        int index = -1;
        //遍历集合修改对应的学生信息
        for (int i = 0; i < array.size(); i++) {
            student ss = array.get(i);
            if (ss.getSid().equals(sid)) {
                //键盘录入要修改的学生新信息
                System.out.println("请输入学生新姓名：");
                String name = sc.nextLine();
                System.out.println("请输入学生新年龄：");
                String age = sc.nextLine();
                System.out.println("请输入学生新居住地：");
                String address = sc.nextLine();

                //创建学生对象
                student s = new student();
                s.setSid(sid);
                s.setName(name);
                s.setAge(age);
                s.setAddress(address);

                array.set(i,s);
                System.out.println("修改学生信息成功！");
                index = i;
                break;
            }
        }
        if (array.size() == 0 || index == -1) {
            System.out.println("你输入的学号有误，请重新输入！");
        }

    }

    //定义方法，判断学号是否被使用
    public static boolean isUsed(ArrayList<student> array, String sid) {
        boolean flag = false;

        for (int i = 0; i < array.size(); i++) {
            student s = array.get(i);
            if (s.getSid().equals(sid)) {
                flag = true;
                break;
            }
        }
        return flag;
    }
}

———————————————————————————————————————————

import com.Cx330.Student;

public class student {
    private String sid;//学号
    private String name;//姓名
    private String age;//年龄
    private String address;//居住地

    public student(){}

    public  student(String sid,String name,String age,String address){
        this.sid = sid;
        this.name = name;
        this.age = age;
        this.address = address;
    }
    public String getSid(){return sid;}
    public void setSid(String sid){this.sid = sid;}

    public String getName(){return name;}
    public void setName(String name){this.name = name;}

    public String getAge(){return age;}
    public void setAge(String age){this.age = age;}

    public String getAddress(){return address;}
    public void setAddress(String address){this.address = address;}
}

———————————————————————————————————————————