Increasing the number of objects being drawn for a command

I am creating the game pong on processing, I would like to increase or add more balls if a button is pressed (currently have it running through arduino). I have the values being read over to processing however whenever I wright my if statement (if Button == 255) … the balls are added however when let go of the button they are removed. How do i keep the balls on the screen when remove my finger off the button?

Please don‘t post duplicates.