For循环中的Java数组索引超出界限异常

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);
}

Answer 1

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];

Answer 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.

Answer 3

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);
}