get a previous or following element with a indentifier

[marcosol]

I have a robot with an orientation ("up","down","left","right"). He must be able to turn clockwise and counter-clockwise.

My first solution was to write an if-statement for every possible orientation and, depending on the current orientation(saved in a private variable), to simply use a setter to change orientation in both a turnClockwise method as a turnCounterClockwise method. This is not really elegant..

Then I thought that it might be possible to put my elements in an arraylist or something like that and save them in a clockwise sequence like "up","right","down","left".
Then I would use a method to get the next or previous element depending on how i'm turning. But I don't know how to retrieve the last element when my index is zero (or vice versa). This is the case when I turn counter-clockwise from "up" to "left". Is this even possible with an array list or should I use something else? Alternative, more elegant solutions are also welcome.

Thanks!

[DiamondSoul]

I think there's a way to do this with enums but I'm not sure.

What I might do is, rather than have a variable to keep track of direction, have two int variables for x velocity and y velocity of the robot. Depending on the specifics of your problem, this may or may not be a good way of doing it, but here's how you'd do it:

The four directions and their corresponding (xvel, yvel) pairs would be:
right: (1, 0)
down: (0, 1)
left: (-1, 0)
up: (0, -1)

So, to rotate clockwise, you would do the following:

int temp=xvel;
xvel=-yvel;
yvel=temp;

And, to rotate counterclockwise, you would do the following:

int temp=yvel;
yvel=-xvel;
xvel=temp;

If it's necessary for you to have a String ("up", "down", "left", or "right") associated with each direction, then using an enum would probably be better solution, but I don't remember how to do that at the moment.

[marcosol]

thanks man thats a really nice way to solve it!

[marcosol]

Now I'm using int orientation (0,1,2,3) fo up right down left. I'm turning like this

public void turnClockwise (){
assert isValidEnergyLevel((energyLevel-100),getMAX_ENERGYLEVEL());
setOrientation(this.orientation+1);
withdrawEnergy(100);
}
public void turnCounterClockwise (){
assert isValidEnergyLevel((energyLevel-100),getMAX_ENERGYLEVEL());
setOrientation(this.orientation-1);
withdrawEnergy(100);
}

public void setOrientation(int orientation) {
this.orientation = Math.abs(orientation)%4;
}
It fits better with the GUI that I'm using.