类型超类的Arraylist用于保存各种子类类型

The functions in my classes have worked after being tested. The ColorDrop creates a falling drop of specified color. The SpeedDrop of specified speed and so forth. I want to put my drops in a list an mass produce them in the GUI. Drop is the superclass, ColorDrop and SpeedDrop are subclasses that extend the superclass. The code compile, but the GUI is blank. Am i assembling my arraylist wrong? Or am I calling methods on objects of that list incorrectly?The functions in my classes have worked after b