Here are the geometry classes used by my custom 2d game engine. Please post any improvements you make back here
contains:
interface Geometry: all classes implement this one
class Vector2: a 2d vector2. can represent many things
class Box: a box with a position and size
class Circle: a circle with a position and radius
class GameRuntimeException: my runtime exception. you can easily replace GameRuntimeException with RuntimeException in the above files