A Rectangle2DChangeStrategy creates instances of Rectangle2D based on the coordinates of the begin, continuation and end of an action. The behavior is undefined if these three methods are not called on the following order:
(begin -> continue* -> end )*

Most implementations will be creating new rectangles based on an existing one. If the created ones constantly replace the original, this effectively "changes" the rectangle's appearance (note that Rectangle2D instances themselves are immutable !). This interface and its implementations were created to easily allow a GUI user to change an existing rectangle by typical resize and move operations.