i'm recently working on a game (my first one) i want to publish on android, it consists of colored cerles (two colors red and blue) generated randomly, moving top down (bullet behavior), you click on a cercle and some actions occur. but that's not the problem. my problem consists of generating those cercles randomly in the top of the screen, and once the're there they move top down (bullet behavior). how can i do this ?
an image of the concept of the game: