Nullpointer Exception when assigning value to Integer array

Question

This seems a bit strange to me. I created a static Integer array and then I am trying to assign a value to it. But I get a Null pointer exception at the degree[i] = 0 line.

Since I am not reading the value before assigning it, I do not understand why the NullPointer exception.

private static Integer[] degree;
public static void initDegree(int num_of_vertices) throws Exception{
    for (int i = 0; i < num_of_vertices; i++) {
        degree[i] = 0;
    }
}

you have not initialized the array.

Mani
– Mani

2014-04-20 22:04:14 +00:00
Commented Apr 20, 2014 at 22:04 — Mani
– Mani, Commented Apr 20, 2014 at 22:04

DeadChex · Accepted Answer · 2014-04-20 22:05:58Z

3

You need to initialize the array.

ex

degree = new Integer[5];

Otherwise, the array itself is just a null.

answered Apr 20, 2014 at 22:05

DeadChex

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3 Comments

Yathi Over a year ago

Thank you! But how do I initialize it if I do not know the size beforehand?

WelcomeTo Over a year ago

@Yathi use ArrayList

WelcomeTo Over a year ago

@Yathi or initialize it before for loop, like: degree = new Integer[num_of_vertices];

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