void tick() {
		if (playing) {
			// advance the block in current direction.
			fruit.move();
			
			//generates a new fruit when one goes off screen
			if (fruit.pos_y < 0) {
				fruit = new Fruit(COURT_WIDTH, COURT_HEIGHT);
				fruit.move();
			}

			// make the fruit bounce off walls...
			fruit.bounce(fruit.hitWall());
			
			//TODO: modify so that it collides with knife?
			// ...and the mushroom
//			fruit.bounce(fruit.hitObj(poison));

			
			//TODO: Check for game end conditions, i.e piled up
			
			// check for the game end conditions
//			if (square.intersects(poison)) {
//				playing = false;
//				status.setText("You lose!");
//
//			} else if (square.intersects(snitch)) {
//				playing = false;
//				status.setText("You win!");
//			}

			// update the display
			repaint();
		}
	}