Why does Java throw NullPointerException here?

Question

public class Test {

    public int [] x;

    public Test(int N)
    {
       int[] x = new int [N];
       for (int i=0;i

        

Answer 1

 int size=reader.readInt();  // size < 3
 StdOut.println(N.x[3]); // length of x[] less than 3, so x[3] case NullPointException