将增量int分配给arraylist中的元素，Java

Question

So I'm still fairly new to Java and it's also been a while since I've programmed in Java. What I want know is how to assign an integer, like a student number, to an element in an array list. I've got three elements in my arraylist, and each element has to have a 7 digit student number with the 7th digit as the next number in sequence (ex. el 1 with student number 1234567, el 2 with 1234568, el 3 with 1234569). I'm not sure if I'm on the right track or not. This code is a work in progress and there are many things I still have to add or fix. My arraylist is in the next code block titled StudentApp.

public class Student    {

    //fields
    private String firstName;
    private String lastName;
    private int sNumber;
    private String major;
    private double gpa;

    private static int count()  {
        int count = 1234567;
        for (int i = 1; i <= count; i++)    {
            System.out.print(count);
        }
        return count;
    }

    //constructors
    public Student()    {
        firstName = null;
        lastName = null;
        sNumber = 1234567;
        major = null;
        gpa = 0.0;

    }

    public Student(String fName, String lName, int sNumber, String maj, double gpa) {
        firstName = fName;
        lastName = lName;
        sNumber = sNumber;
        major = maj;
        gpa = gpa; 
    }

    //methods

    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    public int getsNumber() {
        for(int sNumber = 0; sNumber >= 7; sNumber++)   {
            int sNumber = 1234567;
            sNumber++ 
        }
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public String getMajor() {
        return major;
    }

    public void setMajor(String major) {
        this.major = major;
    }

    public double getGpa() {
        return gpa;
    }

    public void setGpa(double gpa) {
        this.gpa = gpa;
    }

    @Override
    public String toString() {
        return "S" + sNumber + " " + firstName + " "+ lastName + " " + "(" + major +")" + " " + "gpa:" + gpa;
    }
}

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

public class StudentApp {

    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        ArrayList<Student> names = new ArrayList<Student> ();

        Student student1 = new Student();
        student1.setFirstName("Brian");
        student1.setLastName("Scholl");
        student1.setMajor("CS");
        student1.setGpa(3.5);

        Student student2 = new Student();
        student2.setFirstName("Emily");
        student2.setLastName("Davies");
        student2.setMajor("ME");
        student2.setGpa(3.7);

        Student student3 = new Student();
        student3.setFirstName("Sarah");
        student3.setLastName("Dixon");
        student3.setMajor("EE");
        student3.setGpa(3.8);

        names.add(student1);
        names.add(student2);
        names.add(student3);

        int choice;
        do{
            displayMenu();
            choice = input.nextInt();
            switch(choice)  {
            case 1:
                Student student4 = new Student();

                System.out.print("First name: ");
                String fName1 = input.nextLine();
                System.out.println();
                System.out.print("Last name: ");
                String lName1 = input.nextLine();
                System.out.println();

                System.out.print("Major: ");
                String major1 = input.nextLine();
                System.out.println();
                System.out.print("GPA: ");
                double gpa1 = input.nextDouble();

                student4.setFirstName(fName1);
                student4.setLastName(lName1);
                student4.setMajor(major1);
                student4.setGpa(gpa1);
                names.add(student4);
                break;
            case 2:

                System.out.print("Find student with sNumber S");
                input.nextInt();
                student1.getsNumber();
                //statement on finding a student
                break;
            case 3:
                //statement on deleting a student
                break;
            case 4:
                System.out.println(student1);
                System.out.println(student2);
                System.out.println(student3);
                break;
            case 5:
                names.size();
                break;
            case 6:
                System.out.println("Good bye");
                break;
            default:
                System.out.println("Invalid Selection");
                System.out.println();
                break;
            }
            System.out.println();
        }while(choice != 0 );


    }

    public static void displayMenu()    {
        System.out.println("1. Add a student");
        System.out.println("2. Find a student");
        System.out.println("3. Delete a student");
        System.out.println("4. Display all students");
        System.out.println("5. Display the total number of students");
        System.out.println("6. Exit");
    }

}

Answer 1

Add static attribute (studentNumberSequence) to the Student class with initialize value (eg 1234567) and increase it's value in constructors. You can put the following line in constructors:

sNumber = studentNumberSequence++;

I suggest you to use Map (eg HashMap) instead of ArrayList and apply 'sNumber' as the map key.

Answer 2

There's no reason to try to do this the way you are. Consider that you can simply define an initial student number; according to your code I would assume this would be int studentNumber = 1234567; .

Now, when you add a student to the list don't neglect to add that number or initialize all students with the same number; that's just going to over complicate things.

Given that you now have a number, get the other information from the user and add a new Student with those values plus the student number that you assign for them. For example:

names.add(new Student(firstName, lastName, studentNumber++, major, gpa));

Additionally, you have a number of other issues that I won't address here but warn you about.

1. The count should not come from a student instance.
2. Getting the student number should just give the student number (now that you have that figured out)
3. Take care when you're naming constructor parameters the same as the instance variables; you need to distinguish between them somehow.
4. You can't hardcode the outputting of all students; they can add more.