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
– Rohit Jain, Commented Apr 8, 2015 at 5:43
You have to initialize an object before you can use the methods — PoisonedYouth
– PoisonedYouth, Commented Apr 8, 2015 at 5:45
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
– Naveen Ramawat, Commented Apr 8, 2015 at 5:45
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
– ajb, Commented Apr 8, 2015 at 5:46
Sorry for the trouble, I just thought that it would automatically instantiate each of the locations — user4736652
– user4736652, Commented Apr 8, 2015 at 5:48

Ori Lentz · Accepted Answer · 2015-04-08 05:44:31Z

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 8, 2015 at 5:44

Ori Lentz

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2 Comments

user4736652 Over a year ago

Do you know how I can do that in a simple command rather than typing it all out? Btw, thanks alot.

Ori Lentz Over a year ago

Yeah, you can do Arrays.fill(info, new Info()) and it will instantiate all elements in the array.

Kick Buttowski · Accepted Answer · 2015-04-08 05:50:18Z

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 8, 2015 at 5:50

Kick Buttowski

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answered Apr 8, 2015 at 5:46

Daniel Petrov

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