How to create an array with incremented values in Java?

Question

I accepted the input from the user and stored it in the variable "n". But, when I try to execute this code, I get java.lang.NullPointerException.

public class JavaApplication58 {

    public static void main(String[] args) {
        int a[] = null;
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        for (int i = 1; i < n; i++) {
            a[i - 1] = i;
        }
        for (int i = 0; i < a.length; i++) {
            System.out.println("" + a[i]);
        }
    }
}