How to initialise a BigInteger array in the same way like an int[ ] in Java?

Question

In the following code, I am unable to initialize the BigInteger array due to which a NullPointerException is thrown as I compile:

public class Solution {
public static BigInteger[] arr;
public Solution(int n){
    arr=new BigInteger[n];
    for(BigInteger each:arr){
        each=BigInteger.ZERO;
    }
}
public static BigInteger maxlist(){
    BigInteger max=arr[0];
    for(BigInteger elem:arr)
        if(elem.compareTo(max)>0)
            max=elem;
    return max;
}
public static void main(String[] args) {
    Scanner in = new Scanner(System.in);
    int n = in.nextInt();
    int m = in.nextInt();
    Solution s=new Solution(n);
    for(int a0 = 0; a0 < m; a0++){
        int a = in.nextInt();
        int b = in.nextInt();
        BigInteger k = in.nextBigInteger();
        for(int i=a-1;i<=b-1;i++)
        arr[i]=arr[i].add(k);   //Error is thrown here
    }
    System.out.println(maxlist());
    in.close();
}

}

Error: Exception in thread "main" java.lang.NullPointerException at Solution.main(Solution.java:29)

Is there any other way to do it?

Are you providing any input here `BigInteger k = in.nextBigInteger();`? Probably `k` is getting the null value there. — Shridhar R Kulkarni, Feb 17 '18 at 10:23
This wouldn't work with an `int[]` either, but there the values default to `0` as it is an array of a primitive type. — Mark Rotteveel, Feb 17 '18 at 10:33
Moderators..Can you please tell me where is the question asked before marking it duplicate? — Vinay, Feb 17 '18 at 10:36
@Vinay: You can see that at the top of the question you posted. — Shridhar R Kulkarni, Feb 17 '18 at 14:45

Peter Kramer · Answer 1 · 2018-02-17T10:27:57.880

1

Your array initialization is incorrect.

for(Type obj : arr) {
   // in this context, obj does not refer to a part of the array.
   // obj is an iteration variable, assigning values to obj will not affect the array.
}

You need to assign to the array via the indices instead:

for(int i = 0; i < arr.length; i++) {
   arr[i] = BigInteger.ZERO;
}

Your full constructor should look something like this:

public Solution(int n){
    arr = new BigInteger[n];
    for(int i = 0; i < n; i++){
        arr[i] = BigInteger.ZERO;
    }
}

edited Feb 17 '18 at 10:27

answered Feb 17 '18 at 10:23

Peter Kramer

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Do you mean by using valueOf()?Can you elaborate? – Vinay Feb 17 '18 at 10:26
I've edited my answer to clarify. Look at your Constructor code, that's where your issue is :) – Peter Kramer Feb 17 '18 at 10:26
Ohh..But i am fond of Foreach Loop. Can it be done using foreach?? – Vinay Feb 17 '18 at 10:30
No, as I explained, foreach takes each reference from the array and places it in a temporary iteration variable once. Updating iteration variables does not have any effect. – Peter Kramer Feb 17 '18 at 10:32
Yeah. Now I get it.. – Vinay Feb 17 '18 at 10:34

How to initialise a BigInteger array in the same way like an int[ ] in Java?

1 Answers1