Collision

a.getWidth()

a.getImage().getWidth()

a.getHeight()

a.getImage().getHeight()

/**
 * Method act:
 * checks for keypresses and moves the robot the appropriate speed until it comes upon a barrier
 */
public void act() 
{
    move();
}

/**
 * Method move:
 * checks for keypresses and turns and moves the robot
 */
private void move()
{
    int dr = 0;
    if (Greenfoot.isKeyDown("left")) dr--;
    if (Greenfoot.isKeyDown("right")) dr++;
    if (dr != 0)
    {
        turn(dr);
        if (getOneIntersectingObject(Barrier.class) != null) turn(-dr);
    }
    int d = 0;
    if (Greenfoot.isKeyDown("up")) d++;
    if (Greenfoot.isKeyDown("down")) d--;
    int x = getX(), y = getY();
    if (d != 0)
    {
        for (int i=1; i<= speed; i++)
        {
            setLocation(x, y);
            move(d*i);
            if (getOneIntersectingObject(Barrier.class) != null)
            {
                setLocation(x, y);
                move(d*(i-1));
                return;
            }
        }
    }
}