Just click on the canvas to create new balls.

bouncing balls

Ball[] balls = new Ball[1];

void setup() {
  size(200, 200);
  balls[0] = new Ball(50, 100, 16, 0.1);
}

void draw() {
  background(0);
  for ( int i = 0; i < balls.length; i++ ) {
    balls[i].display();
    balls[i].move();
  }
}

void mousePressed() {
  Ball b = new Ball(mouseX, mouseY, 16, 0.1);
  balls = (Ball[]) append(balls, b);
} 

class_Ball

class Ball {
  
  float x;
  float y;
  float speed;
  float w;
  float gravity;
  
  Ball( float temp_x, float temp_y, float temp_w, float temp_gravity ) {
    x = temp_x;
    y = temp_y;
    w = temp_w;
    speed = 0;
    gravity = temp_gravity;
  }
  
  void display() {
    fill(255);
    noStroke();
    ellipseMode(CENTER);
    ellipse(x,y,w,w);
  }
  
  void move() {
    y = y + speed;
    speed = speed + gravity;
    if ( y > height ) {
      speed = speed * -0.95;
    }
  }
  
}