How to have a ArrayList with a unique ID

Question

i created an Arraylist of Student objects. i am using a static variable as an ID.

this is what my Student class looks like;

Student class

And the Runner file looks like;

Runner file

the output i receive is;

St_ID St_Name St_Age St_Course 3 James 23 Statistics 3 Mick 24 Biology 3 Jenni 22 Literature

but what i require is;

St_ID St_Name St_Age St_Course 1 James 23 Statistics 2 Mick 24 Biology 3 Jenni 22 Literature

Don't use a static value - or, reassign the running value to a non-static variable, so you would have a "generator" which would generate the next value, but that value need to be assigned to an instance field of your class — MadProgrammer, Jan 07 '18 at 05:30
Please do NOT post pictures of code, include the code directly. Please visit the [help] and read [ask]. — Jim Garrison, Jan 07 '18 at 05:30
Follow the link https://stackoverflow.com/questions/17547360/create-an-arraylist-of-unique-values — Kedar Km, Jan 07 '18 at 05:44
Do the ids have to be starting from 1 and counting up? Because if you call hashcode() on your student class instances it will give you a unique number to identify your students by. — Meepo, Jan 07 '18 at 06:00

score 1 · Accepted Answer · answered Jan 07 '18 at 07:35

1

You are right about the count variable being static. However, the Student class should also have a field that stores the id of each student. This should be non-static since each student is going to have a different one.

private int id;

In the constructor, assign count to it:

count++;
id = count;

The getId method should be non-static and return id:

public int getId() { return id; }

answered Jan 07 '18 at 07:35

Sweeper

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Thank you Sweeper, finally got it working, i appreciate your help. – ThivankaW Jan 08 '18 at 06:14
@ThivankaW if you think my answer answers your question, please consider accepting it by clicking on the check mark! – Sweeper Jan 08 '18 at 06:45

score 0 · Answer 2 · answered Jan 07 '18 at 06:05

If all you cant is a unique id, calling stobj.hashCode() will return a unique hashcode, so each student has a unique id. However, if you need the ids to start at 1 and count up, then keep the count, but also make a non-static variable and set it equal to the current count in the constructor.

public class Student {
    //fields here
    private static int count = 0; //not good style, but whatever
    private int id;

    public Student(String n, int a, String c) //you should work on your variable names
        count++;
        id = count;
        //other stuff here

Thank you so much Meepo, it worked. thanks for the constructive answer. — ThivankaW, Jan 08 '18 at 06:11

How to have a ArrayList with a unique ID

2 Answers2