Hello, Please check the sketch at https://www.openprocessing.org/sketch/851540 it seems that when run in openprocessing.org it passes but a few iterations of the while() loop of the getRandom() method, but it prints that the size() of ArrayList candidates decreases. when run from the processing i…

The wording of your post is not clear. You express some things don’t work and you need help, in a nutshell. Let’s take a step back. Please explain what your code suppose to do, what it does right now (unintended behavior) and where are the culprit lines. Any theories? On a side note, I tried runni…

Ok. My bad, sorry. What it’s supposed to do: Generate a list of random points on the screen at a minimal distance from each other but as tight as possible. The algorithm is as follows: Make a list of all possible places where a point can be placed, name the list candidates. While the candidates…

mmm I don’t get exactly what you want, but using ArrayList, if you want to remove all the list, I use mylist.clear , and if you want to remove one from the list I use mylist.remove(posOfTheElementIWantToRemove) :sweat_smile: Hope this helps you in something

removeAll() method removes a collection from another collection. see https://docs.oracle.com/javase/8/docs/api/java/util/ArrayList.html#removeAll-java.util.Collection- not clear(), not remove(), but something in between :slight_smile: thanks for your interest!

Quick glance and first guess: Why is getNeighbors() creating an ArrayList of new Loc objects? When in getRandom() you use `removeAll(), it should check for the same elements to remove, shouldn’t it? But these aren’t the same elements – they are new elements that you just created. Instead, you get s…

I see… So it compares by reference, not by value. I guess I’ll have to rewrite it into ArrayList<Int> instead of ArrayList<Loc>. Thank you, @jeremydouglass But I wonder how it happens to work in the browser…

[image] LuckSmith: So it compares by reference, not by value. Not exactly, but the default equals and hashCode methods will. Have you overridden them? See https://www.baeldung.com/java-equals-hashcode-contracts

I have implemented equals() but not hashCode(). The article you gave says both are essential.

Yes, equal objects should have equal hashcodes. Although that’s only important for certain types of collection. You might get away with just equals. I would also double check your equals method is returning true in all cases you think it should.

Just a suggestion – it might be easier to make getNeighbors actually get the neighbors. Then removeAll would remove them correctly.

Can't find a mistake or removeAll() doesn't work

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Can't find a mistake or removeAll() doesn't work

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