Simple student management system

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

public class studentDemo {


    public static void main(String[] args) {
        ArrayList<student> array = new ArrayList<student>();
        Scanner sc = new Scanner(System.in);
        int i = 0;
        do {
            System.out.println("------- Welcome to the student management system -------");
            System.out.println("1. Add student ");
            System.out.println("2. Delete students ");
            System.out.println("3. Revise students ");
            System.out.println("4. Check out all the students ");
            System.out.println("5. sign out ");
            System.out.println(" Please enter your choice ：");
            i = sc.nextInt();
            if (i == 1) {
                toAdd(array);
            } else if (i == 2) {
                toRemove(array);
            } else if (i == 3) {
                toSet(array);
            } else if (i == 4) {
                toGet(array);
            }
            else if(i!=5){
                System.out.println(" The choice you entered is wrong , Please re-enter ！！！");
            }

        }
        while (i != 5);
        System.out.println(" Thank you for using. ！！！");
    }

    public static void toRemove(ArrayList<student> array) {
        Scanner sc = new Scanner(System.in);
        System.out.println(" Please enter the name of the student you want to delete ：");
        String name = sc.nextLine();
        for (int i = 0; i < array.size(); i++) {
            student s = array.get(i);
            if (s.getName().equals(name)) {
                array.remove(i);
                System.out.println(" Delete student information successfully ！！！");
                return;
            }
        }
        System.out.println(" Check no one , Please re-enter the information ！！！");
    }

    public static void toSet(ArrayList<student> array) {
        Scanner sc = new Scanner(System.in);
        System.out.println(" Please enter the name of the student you want to modify ：");
        String name = sc.nextLine();
        for (int i = 0; i < array.size(); i++) {
            student s2 = array.get(i);
            if (s2.getName().equals(name)) {
                student s = new student();
                System.out.println(" Please enter the new name of the student you want to modify ");
                s.setName(sc.nextLine());
                System.out.println(" Please enter the new age of the student you want to modify ：");
                s.setAge(sc.nextLine());
                System.out.println(" Please enter the new student number of the student you want to modify ：");
                s.setId(sc.nextLine());
                System.out.println(" Please enter the new address of the student you want to modify ：");
                s.setDi(sc.nextLine());
                array.set(i, s);
                System.out.println(" The information was modified successfully ！！！");
                return;// End this method directly 
            }
        }
        System.out.println(" Check no one , Please re-enter the information ！！！");
    }

    public static void toGet(ArrayList<student> array) {
        // toGet(array);
        //   \t: In fact, that is tab Key position 
        //  Shortcut key ：ctrl+alt+l： formatting code 
        if (array.size() == 0) {
            System.out.println(" No information , Please add information before querying ！！！");
            // It's OK in the back here + return;----- It means to end 
        } else {
            System.out.println(" The student's name \t Student age \t Student student id \t Student address ");
            for (int j = 0; j < array.size(); j++) {
                student s = new student();
                s = array.get(j);
                System.out.println(s.getName() + "\t" + s.getAge() + " year \t" + s.getId() + "\t\t" + s.getDi());
            }
        }
    }

    public static void toAdd(ArrayList<student> array) {
        Scanner sc = new Scanner(System.in);
        student s = new student();
        String name;
        while (true) {
            System.out.println(" Please enter the name of the added student ：");
            name = sc.nextLine();
            boolean flag = isUsed(array, name);
            if (flag) {
                System.out.println(" The student name you entered is already occupied , Please re-enter ！！！");
            } else {
                break;
            }
        }
        System.out.println(" Please enter the age of the added student ：");
        String age = sc.nextLine();
        System.out.println(" Please enter the student ID of the added student ：");
        String id = sc.nextLine();
        System.out.println(" Please enter the address of the added student ：");
        String di = sc.nextLine();
        s.setName(name);
        s.setAge(age);
        s.setId(id);
        s.setDi(di);
        array.add(s);
        System.out.println(" Add student successfully ！！！");

    }

    public static boolean isUsed(ArrayList<student> array, String name) {
        boolean flag = false;
        for (int i = 0; i < array.size(); i++) {
            student s = array.get(i);
            if (s.getName().equals(name)) {
                flag = true;
                break;
            }
        }
        return flag;
    }
}
 class student {
    private String name;// name 
    private String age;// Age 
    private String id;// Student number 
    private String di;// Address 

    public student() {
    }
// Shortcut key ：alt+ins---- Methods can be constructed quickly 

    public student(String name, String age, String id, String di) {
        this.name = name;
        this.age = age;
        this.id = id;
        this.di = di;
    }

    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 getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getDi() {
        return di;
    }

    public void setDi(String di) {
        this.di = di;
    }
}