Why am i getting a java.lang.NullPointerException in my program? I don't see any thing wrong with it

Question

It is program to find the largest prme factor of any number.

// Program to get the largest prime factor of a number

import java.util.*;

class factor{

    ArrayList<Long> a;

    public void large(long n){
        for(long i = 1; i <= n; i++){
            if (n % i == 0){
                a.add(i);
            }   
         }
        System.out.println(Collections.max(a));
   }
}

class test{
     public static void main(String[] args){
         factor g = new factor();
         g.large(13195);
     }
}

You haven't initialized `a`. This is trivially obvious. Not that you even need it. The program would work better without it. — user207421, Apr 20 '17 at 10:35

score 0 · Answer 1 · answered Apr 20 '17 at 10:36

You need to initialize your list, before invoking any method on it.

class Factor{

    List<Long> a = new ArrayList<>();

    public void large(long n){
        for(long i = 1; i <= n; i++){
            if (n % i == 0){
                a.add(i);
            }   
         }
        System.out.println(Collections.max(a));
   }
}

Why am i getting a java.lang.NullPointerException in my program? I don't see any thing wrong with it

1 Answers1