public void move(int xa, int ya) {
        if (xa != 0 && ya != 0) {
            move(xa, 0);
            move(0, ya);
            return;
        }
        
        if(!moved) {
        	moved = true;
        }

        if (!collision(xa, ya)) {
            x += xa;
            y += ya;
        }
    }