ArrayList an ArrayList?? Overlapping balls.

Programming Questions

miles.tone

ArrayList an ArrayList?? Overlapping balls.

in Programming Questions • 2 years ago

I have an arrayList of clickable balls, i don't mind them overlapping, but its a problem when they clump when clicked or when a smaller ball is obscured by a larger one. What would be the best way to sort this?

an array list of the balls ordered by size so they are drawn in order?

Many Thanks

Miles

Replies(8)

PhiLho

Re: ArrayList an ArrayList?? Overlapping balls.

2 years ago

You can easily sort an array list on a given criterion. Search Comparator and Comparable on the Processing site.

fiveagon

Re: ArrayList an ArrayList?? Overlapping balls.

2 years ago

Yeah, in your Ball class, if that is what you call it, you can implement Comparable and make the method compareTo()

class Ball implements Comparable<Ball>
{
float r; // radius
// ...
float getSize() {
return r;
}
int compareTo(Ball otherBall) {
if (this.getSize() < otherBall.getSize()) { // You want smaller Balls to be drawn last, right?
return 1;
}
else if (this.getSize() == otherBall.getSize()) { // Will almost never be true with floats.
return 0;
}
else {
return -1;
}
}
//...
} // class Ball implements Comparable<Ball>

or even simpler:

public int compareTo(Ball otherBall) {
// What's the best way to do this if ballSize is a float?
return otherBall.ballSize - this.ballSize;
}

Then you can use the static Collections class to sort your ArrayList<Ball>

Collections.sort(ballList);

This is untested, so let me know if this doesn't work.

PhiLho

Re: ArrayList an ArrayList?? Overlapping balls.

2 years ago

About floats:
You define a tolerance on the values, and return zero if the absolute value of the difference of the compared values is below this tolerance (eg. 0.1 or lower for values between 1.0 and 10.0). This is because floating point calculations are inherently imprecise, so f1 == f2 is likely not to work.
If not equal by this method, just return 1 or -1 with the inequality test you show above.

miles.tone

Re: ArrayList an ArrayList?? Overlapping balls.

2 years ago

Thank you guys,

Whats the best way to call the "other ball" and the ".ballsize" part?

Also the public call can go anywhere, is that right?

Im shocking with arrays and array lists.

Would it be useful if i put up some code?

Thats really interesting PhiLho, where does the variation/imprecision come from?

Cheers

Miles

fiveagon

Re: Re: ArrayList an ArrayList?? Overlapping balls.

2 years ago

Whats the best way to call the "other ball" and the ".ballsize" part?

You don't need to worry about the otherBall nor the compareTo() method in your main program at all. The Collections class will take care of that when it does the sort.

Probably to make a getSize() method for your ball class and use that in the first compareTo() method in my post earlier.

public float getSize() {
return ballSize; // Where ballSize is a class variable of Ball
}

Phi.lho brought up a great point ab out precision. I was wondering how to do the simpler version of compareTo() with floats. In this instance, I don't think we need to worry about precision.

Also the public call can go anywhere, is that right?

Anywhere inside your Ball class. Make sure you implement Comparable as I described earlier.

Post the code of your Ball class with these changes. If it's still not happening, I'll be glad to shine some light on anything you don't understand.

PhiLho

Re: ArrayList an ArrayList?? Overlapping balls.

2 years ago

Imprecision comes from the way floating point numbers (which can theoretically can have an infinite number of decimal digits, see PI) are represented in the binary format. Precision is limited, so rounding errors happen.

miles.tone

Re: ArrayList an ArrayList?? Overlapping balls.

2 years ago

It works perfectly, thank you very much.

You definitely just saved me a massive ball ache.

fiveagon

Re: Re: ArrayList an ArrayList?? Overlapping balls.

2 years ago

Definitely don't want any ball aches around here.

I edited my first post above to put in all the relevant bits.

phi.lho, any chance you could change the thread title to "How to sort an ArrayList?".

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