Null Pointer Exception from class array

Question

I want to make an array of size 150 of the class Info

public class Info {
    int Group;
    String Name;
}

But I have the exception occur after

 public class Mover {
        static Info[] info=new Info[150];
            public static void main(String[] args) {
            info[0].Group=2;//I get error here
        }
}

I'm not sure if there is a better way to do what a want to do, but I don't want to use a multidimensional array. I'm simply trying to add information to the group, so I'm confused.

First you've to create `Info` object, then only you can set value to its attribute. — Rohit Jain, Apr 08 '15 at 05:43
You have to initialize an object before you can use the methods — poisonedYouth, Apr 08 '15 at 05:45
Assign objects in your array ... currently info[0] ... info[n] are null and any operation on these array elements will lead to NPE — Naveen Ramawat, Apr 08 '15 at 05:45
This really should be marked as a duplicate of something, but I can't find any of the other 15,326 questions that have asked this. — ajb, Apr 08 '15 at 05:46
Sorry for the trouble, I just thought that it would automatically instantiate each of the locations — Avionix, Apr 08 '15 at 05:48

score 1 · Answer 1 · answered Apr 08 '15 at 05:44

1

doing new Info[150] simply instantiates an array of size 150. All elements within the array have not been instantiated and are therefore null.

So when you do info[0] it returns null and you're accessing null.Group.

You have to do info[0] = new Info() first.

answered Apr 08 '15 at 05:44

Ori Lentz

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Do you know how I can do that in a simple command rather than typing it all out? Btw, thanks alot. – Avionix Apr 08 '15 at 05:46
Yeah, you can do `Arrays.fill(info, new Info())` and it will instantiate all elements in the array. – Ori Lentz Apr 08 '15 at 05:51

score 0 · Answer 2 · edited Apr 08 '15 at 05:50

0

This static Info[] info=new Info[150]; is creating an array of 150 objects of type info pointing to NULL. You have to do this to get this working

for(int i = 0; i< 150; i++) info[i] = new Info();

Then you can use these objects

edited Apr 08 '15 at 05:50

Kick Buttowski

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answered Apr 08 '15 at 05:46

Daniel Petrov

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score 0 · Answer 3 · edited Apr 08 '15 at 05:50

0

Go through some tutorial first Java Arrays

You need to initialize the array elements like:

info[0] = new Info()

From JLS 10.6. Array Initializers

An array initializer may be specified in a declaration (§8.3, §9.3, §14.4), or as part of an array creation expression (§15.10), to create an array and provide some initial values.

edited Apr 08 '15 at 05:50

Andy Turner

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answered Apr 08 '15 at 05:46

Sumit Singh

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Null Pointer Exception from class array

3 Answers3