Java Array Index Out of Bounds Exception in For-loop

Question

I am making a program that runs a formula on the numbers inputted. The first integer in the input describes the amount of lines, or integers to be used in the formula. I am approaching this by calculating the answers and pushing them into an array. However, I am getting an array out of bounds exception in one of my for loops, and I can't figure out why.

Here is my main method:

    public static void main(String[] args) {
    Scanner scan = new Scanner (System.in);
    int[] nums = {};
    int lines = scan.nextInt();
    for(int i = 0; i < lines; i++){
        nums[i] = potFormula(scan.next());
    }
    System.out.println(nums);
}

Looks like you need to initialize the nums array to the length of lines — Blue Boy, Dec 14 '16 at 21:51
As an aside, once you fix the array issue, you'll find that your print statement doesn't do what you want. See http://stackoverflow.com/questions/409784/whats-the-simplest-way-to-print-a-java-array — Sam, Dec 14 '16 at 22:05

score 4 · Answer 1 · answered Dec 14 '16 at 21:52

4

Arrays have a fixed size that can't be changed once allocated. You're initializing nums to {}, which is an empty array. Its size will always be zero.

Instead, you could use:

int lines = scanner.nextInt();
int[] nums = new int[lines];

answered Dec 14 '16 at 21:52

Sam

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score 2 · Answer 2 · answered Dec 14 '16 at 21:52

2

Your array is too small (it has zero elements). Here is one way to fix this:

int lines = scan.nextInt();
int[] nums = new int[lines];

This approach works since you know the size in advance. If you didn't, you could use an ArrayList<Integer>. Array lists have the ability to grow on demand.

answered Dec 14 '16 at 21:52

NPE

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plus 1 for mentioning ArrayList! – Haifeng Zhang Dec 14 '16 at 21:55
@HaifengZhang although since the number of items is known in advance, an ArrayList might just be unnecessary overhead. – Sam Dec 14 '16 at 22:04

score 1 · Answer 3 · answered Dec 14 '16 at 21:52

You need to initialize the nums array to the length of the lines,

Like this:

public static void main(String[] args) {
    Scanner scan = new Scanner (System.in);
    int lines = scan.nextInt();
    int[] nums = new int[lines];
    for(int i = 0; i < lines; i++){
        nums[i] = potFormula(scan.next());
    }
    System.out.println(nums);
}

Java Array Index Out of Bounds Exception in For-loop

3 Answers3