Mover mover;

void setup() {
	size(200,200);
	smooth();
	background(255);
	mover = new Mover(); 
}

void draw() {
	noStroke();
	fill(255,10);
	rect(0,0,width,height);
	mover.update();
	mover.checkEdges();
	mover.display(); 
}

class Mover {
	PVector location;
	PVector velocity;

	Mover() {
		location = new PVector(width/2, height/2);
		velocity = new PVector(0, 0);
	}

	void update() {
		velocity = new PVector(random(-2,3),random(-2,3));
		location.add(velocity);
	}

	void display() {
		stroke(0);
		fill(175);
		ellipse(location.x,location.y,16,16);
	}

	void checkEdges() {
		if (location.x > width) {
			location.x = 0;
		} else if (location.x < 0) {
			location.x = width;
		}   
		if (location.y > height) {
			location.y = 0;
		} else if (location.y < 0) {
			location.y = height;
		}
	}
}