/**
* Add obstacles around the edges of the screen.
*/
private void addEdgeObstacles() {
final int width = 30;//edge obstacle width
obstacles.add(new RectangleObstacle(0 - width, 0 - width, width, HEIGHT + width * 2));//left side
obstacles.add(new RectangleObstacle(WIDTH, 0 - width, width, HEIGHT + width * 2));//right side
obstacles.add(new RectangleObstacle(0, 0 - width, WIDTH, width));//top
obstacles.add(new RectangleObstacle(0, HEIGHT, WIDTH, width));//bottom
}