Using an array as an attribute to modify it Java

Question

my friend has programmed a Breakout game in java. I know C++, which tranfers relatively well to java.

I had a problem when trying to insert a MultiBall brick.

Here are the relevent bits of my function:

private Balle[] balle;
public BriqueMultiBalle(Balle[] bal) {
        super();
        balle = bal;
        SCORE = 100;
    }
public void touched() {
        visible = false;
        balle[Balle.getNInstance()].makeVisible();
    }

I get no error but I found out when debugging that balle corresponds to a null pointer. I tried using these different declarations, however, none of them worked:

1.

    public BriqueMultiBalle(Balle[] bal) {
                super();
                for(int i = 0; i < 6; i++)
                    {
                         balle[i] = bal[i];
                    }
                SCORE = 100;
            }

2.

public BriqueMultiBalle(Balle[] bal) {
            super();
            balle = new Balle[](bal);
            SCORE = 100;
        }

However, these methods do not work.

Thanks,

Ghi102

Which constructor are you calling, the default, or the one where you pass in a Balle[]? If the latter, are you sure you're passing in an initialized Balle[]? — Justin Jasmann
– Justin Jasmann, Commented Jun 20, 2014 at 19:28
How are you creating the Balle[] that you're passing in to the constructor? Perhaps you can show us the code where you do this? — Dawood ibn Kareem
– Dawood ibn Kareem, Commented Jun 20, 2014 at 19:44

Mike Elofson · Accepted Answer · 2014-06-20 19:45:27Z

1

You are getting a null pointer on balle because you never initialize the array, you leave it as

private Balle[] balle;

Try initializing you code

balle = new Balle[bal.length];
for(int i = 0; i < bal.length; i++){
        balle[i] = bal[i];
}

Here's an example I wrote using an int array. Same concept, just apply it to your object.

public static void main(String[] args) throws Exception {

    int[] arrayInts;
    int[] originalInts = { 1, 2, 3, 4, 5 };

    arrayInts = new int[originalInts.length];

    for(int i = 0; i < originalInts.length; i++){
        arrayInts[i] = originalInts[i];
    }

    originalInts[0] = 10;
    for (int i : arrayInts) {
        System.out.println(i);
    }
}

answered Jun 20, 2014 at 19:45

Mike Elofson

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