Null pointer exception when passing instantiated objects to method

Question

I have a simple class where the constructor creates an array of objects, and obtain the hash code of each object in the array, as following. At run time, the program throws a null pointer exception when System.identityHashCode(Object x) is called. I have already instantiated the Object. Why might the exception have occurred?

public class ArrayOfObjects 
{
    private Object[] array;
    private int[] arrayIdentity;

    public ArrayOfObjects(int N)
    {
        array = new Object[N];
        for (int i = 0; i < N; i ++)
        {
            array[i] = new Object();
            **// The line below throws null pointer exception.**
            arrayIdentity[i] = System.identityHashCode(array[i]); 
        }
    }

    public static void main(String[] args) 
    {
        ArrayOfObjects arrayOfObjects = new ArrayOfObjects(10);  

        // Do something.
    }
}

Answer 1

You need to instantiate arrayIdentity also:

array = new Object[N];
arrayIdentity = new int[N];