You will need to track which direction the ship is currently moving. The speed is a constant and can be hard-coded or held in a field. The new y-coordinate of the ship in your setLocation line can then be expressed as 'getY()+dir*speed' or 'getY()+dir*5', for example. The 'dir' field, as an int, would hold a value of '1' or '-1' to add or subtract the speed value. A separate set of code lines will be needed to negate the value of the 'dir' field when conditions are right. The condition could be at specific y-coordinate values or a counter field can be used to limit the number of moves in either direction.