public class CollectionPolygon extends SimplePolygon
{
    private List<Vertex2D> vertices = new ArrayList<Vertex2D>();
    /**
     * Constructor for objects of class CollectionPolygon
     */
    public CollectionPolygon(Vertex2D[] vertArray)
    {
        if (vertArray == null)
            throw new NullPointerException("Array is null.");

        for (int i = 0; i < vertArray.length; i++)
        {
            if (vertArray[i] == null)
            {
                throw new NullPointerException(i +" in array is null.");
            }
            else
            {
                vertices.add(vertArray[i]);
            }
        }
    }
    public int getNumVertices(){
        return vertices.size();
    }
    public Vertex2D getVertex(int index){
        if (index < 0)
            throw new IllegalArgumentException("Index cant be negative.");

        return vertices.get(index % this.vertices.size());
    }

    public Collection<Vertex2D> getVertices(){
        return Collections.unmodifiableList(vertices);

    }
    public CollectionPolygon invert(){
        List<Vertex2D> reversed = new ArrayList<Vertex2D>();
        for ( int i = vertices.size() - 1; i >= 0; i-- )
        {
           Vertex2D obj = this.vertices.get( i ) ;
           reversed.add( obj ) ;
        }
        Vertex2D[] reversedArray = new Vertex2D[reversed.size()];
        reversedArray = reversed.toArray(reversedArray);
        CollectionPolygon reversedPolygon = new CollectionPolygon(reversedArray);
        return reversedPolygon;

    }