Why does my code seem like it's not checking that students.size() > 0 before the rest of the if statement?

Question

I'm new to using array lists and would like to ask why I am getting an index out of bounds exception when I explicitly state that my students array list must be larger than zero before trying to access it in my if statement on line 23.

I am not sure what I am doing wrong and could really use some help. Thank you.

My code:

import java.util.Scanner;
import java.util.ArrayList;
public class Test {

public static void main(String[] args) {
    Scanner input = new Scanner(System.in);
    ArrayList<Student> students = new ArrayList<Student>();
    String name = "";
    int age = 0;
    int GPA = 0;
    boolean running = true;

    while(running) {
        name = input.next();
        if(name.equals("next") && students.size() > 0) {
            students.remove(0);
            continue;
        } else if(name.equals("end")) {
            running = false;
        }
        age = input.nextInt();
        GPA = input.nextInt();
        Student newStudent = new Student(name, age, GPA);
        if(students.size() > 0 && age < students.get(students.size() - 1).getAge() || GPA < students.get(students.size() - 1).getGPA()) {
            String tempName = students.get(students.size() - 1).getName();
            int tempAge = students.get(students.size() - 1).getAge();
            int tempGPA = students.get(students.size() - 1).getGPA();
            Student tempStudent = new Student(tempName, tempAge, tempGPA);
            students.remove(students.size() - 1);
            students.add(newStudent);
            students.add(tempStudent);
        } else {
            students.add(newStudent);
        }
    }

    if(students.size() == 0) {
        System.out.println("empty");
    } else {
        for(int i = 0; i < students.size(); i++) {
            System.out.println(students.get(i).getName());
        }
    }
}

}

Where did you give the size for your arraylist? you should first provide a value to be checked if it's larger than zero — Vishwa, Jan 25 '18 at 06:23

Kristof · Answer 1 · 2018-01-25T06:21:55.953

3

The array is zero based (the items are indexed 0,1,2,3...n-1 where n is the number of items), so students.get(students.size()) will always fail with an out-of-bounds. It should be students.get(students.size()-1).

edited Jan 25 '18 at 06:21

answered Jan 25 '18 at 06:20

Kristof

104
4

That's what I had before. I just changed it back and now the array index is -1? – Jan 25 '18 at 06:25
That's confusing to me though because I have it check if there's an element in the array before it tries to access it. – Jan 25 '18 at 06:26
If there's 1 item, then 1 -1 == 0, which is the first time of the arraylist. – Kristof Jan 25 '18 at 08:29

score 0 · Answer 2 · answered Jan 25 '18 at 06:30

0

you als should not use while(true) if possible, because its not so elegant. Rather state the condition to continue in brackets.

Are "while(true)" loops so bad?

answered Jan 25 '18 at 06:30

floboe

25
2
8

Okay I fixed that. Thanks for the suggestion. – Jan 25 '18 at 06:33

Why does my code seem like it's not checking that students.size() > 0 before the rest of the if statement?

2 Answers2