Illegal argument exception: n must be positive

Question

main class:

public class ECONAPP2 {
static Scanner input= new Scanner(System.in);
static int score = 0;
static ArrayList used         


        

Answer 1

n represents the parameter of the Random#nextInt(int n) method. The parameter must be a positive integer. In your example, the size of the array could be 0, thus resulting in the exception.

Answer 2

In this line

int randomNumber = generator.nextInt(usedArray.size());

you are trying to generate random number.

However you have empty usedArray, so it returns 0. You cant generate random number in range 0 to 0 exlusive, so it throws exception. The value must be 1 or higher.

Note documentation : "value between 0 (inclusive) and the specified value (exclusive)", so for example generator.nextInt(1) return 0 on all calls, generator.nextInt(2) returns 0 or 1...

Answer 3

You want to change the order you're calling methods in you main method. Try this:

public static void main(String[] args){
    arrayContents();
    app();
}

This way when you call app(), your ArrayList has items in it.