The Rectangle class was created to store relevant information about each rectangle. By using a custom class, we were able to design our rectangles any way we wanted. These rectangles have properties and methods which allow us to easily control their position, size and colour. By adding some smart functionality to each rectangle, we were able to get the rectangle to automatically position and colour itself based on key values.
The Serial library is used to allow communication with the Arduino. In this Processing sketch, the values obtained from the Arduino were converted to floats to allow easy calulations of the beats per minute (BPM). I am aware that I have over-engineered the serialEvent method somewhat, because the Arduino is only really sending two values. I didn't really need to convert the String. But I am happy with the end result, and it does the job