Question

I attempted to adapt a class I had found on the web for a dynamic array of ints for a dynamic array of “Entities,” but now I am getting a “NullPointerException.”

The code raising the exception is:

public void initialize()
{
    buffer = new BufferedImage(800,600,BufferedImage.TYPE_INT_RGB);
    Entities.put(Entities.getCurrentPos()+1, new Entity(100, 100, Color.green));
    Entities.put(Entities.getCurrentPos()+1, new Entity(400, 400, Color.blue));
}

The relevant parts of DynArrayEntities class:

...

private Entity[] data;  // An array to hold the data.
private int currentpos = 0;

...

public void put(int position, Entity value) {

    if (position >= data.length) {

        int newSize = 2 * data.length;
            if (position >= newSize)
                newSize = 2 * position;
        Entity[] newData = new Entity[newSize];
        System.arraycopy(data, 0, newData, 0, data.length);
        data = newData;
    }

    data[position] = value;
    currentpos++;

}

....

public int getCurrentPos() {
    return currentpos;
}

Thanks in advance for your help!

Answer 1

...

private Entity[] data= new Entity[0];  // Or some value > 0
...

otherwise data is null the first time you access it in the method.