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gmacias
gmacias wrote ...

2016/10/5

If Loop or While Loop? Or something different?

gmacias gmacias

2016/10/5

#
In my highway scenario I have a two-lane highway with sand and trees on either side. I would like to program the vehicle so that it brings up a dust cloud object when it goes on the sand (X coordinates <= 185 and >= 430) and the dust cloud disappears when it gets back on the highway ( between coordinates 185 and 430). I thought that a while loop would work but I am sure I am not programming correctly since I am new at this. It compiles but gives an error when the vehicle touches the sand. This is what I have (don't laugh...)
?
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public class Ambulance extends Actor
{
    /**
     * Act - do whatever the Ambulance wants to do. This method is called whenever
     * the 'Act' or 'Run' button gets pressed in the environment.
     */
    public void act()
    {
        drive();
        collision();
        makeDust();
    }   
     
    /**
     * This method keeps the ambulance's rotation to 0
     * degrees unless the right key or left key is
     * pressed. If so, the ambulance will turn 10
     * degrees and move in that direction. If the up or
     * down keys are pressed, the ambulance will move 1
     * pixel in that direction.
     */
    private void drive()
    {
        if (Greenfoot.isKeyDown("right"))
        {
            setRotation(10);
            move(1);
        }
         
        else if (Greenfoot.isKeyDown("left"))
        {
            setRotation (350);
            move(-1);
        }
        else if (Greenfoot.isKeyDown("up"))
        {
            setLocation(getX(), getY()-1);
        }
        else if (Greenfoot.isKeyDown("down"))
        {
            setLocation(getX(), getY()+1);
        }
        else
        {
           setRotation(0);
        }
    }
     
    public void collision()
    {
        if (isTouching (NorthCar.class))
        {
            getWorld().addObject (new Crash(), getX(), getY());
            removeTouching(NorthCar.class);
        }
         
        if (isTouching (SouthCar.class))
        {
            getWorld().addObject (new Crash(), getX(), getY());
            removeTouching(SouthCar.class);
        }
         
        if (isTouching (Trees.class))
        {
            getWorld().addObject (new Crash(), getX(), getY());
            removeTouching(Trees.class);
        }
    }
     
    private void makeDust()
    {
        int i = getX();
         
        while (i <= 185)
        {
            getWorld().addObject(new Cloud(), getX(), getY()+60);
        }
         
        while ( i >= 430)
        {
            getWorld().addObject(new Cloud(), getX(), getY() + 60);
        }
    }
}
danpost danpost

2016/10/5

#
If you think about the execution of lines 74 through 77 and of lines 79 through 82, you will see that since the location of the ambulance does not change while the loops execute, the loop will never be exited. Therefore, you will continually create cloud objects (one overtop of another) until memory is used up. Using 'if' is sufficient in both places (lines 74 and 79 -- instead of 'while'). It would be best to have your cloud object have a short lifespan. For one thing, so you do not have too many actors which can cause lagging; and for another, so when the car gets back off the sand, they fade and disappear. This would be similar to the Smoke class which greenfoot has a tutorial on.
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