Java - Sorting Arraylist by an objects instances.

Question

I've created a tournament ranking program which has two classes so far. A Team class and a Scoring class. The team class holds instance variables such as a elo score (double) based on win/loss/ties. The Scoring class takes an arraylist of Teams and the plan is to create a new Arraylist of teams in order from highest elo to lowest elo.

My question is, what would be the best way and how would I sort the teams based on elo ranking and add them to the new Arraylist.

Well, why don't you try something and see how it goes? There are a *lot* of sorting questions on SO, and I'm sure you'd be able to find something helpful without you needing someone to tell you exactly what to do. — awksp, Jul 02 '14 at 22:58

score 0 · Answer 1 · answered Jul 02 '14 at 22:58

0

Here is one way:

class Scoring{

private ArrayList<Team> teams;



public void addTeams(ArrayList<Team> toAdd){

for(Team t : toAdd){
for(int i = 0; i < teams.size(); i++){
if(teams.get(i).elo<t.elo)break;
}
teams.add(i, t);
}

}

}

Another way to do this, would be to create a comparitor, and sort the arraylist toAdd using that comparitor, then adding it to teams.

answered Jul 02 '14 at 22:58

Dean Leitersdorf

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OP's asking for how to sort the list but you're not providing that in your answer. Also, you can use `List#addAll(Collection)` and remove all that code in the `addTeams` method. – Luiggi Mendoza Jul 02 '14 at 23:00
Yes I am, the teams will all be entered in a sorted manner. As long as all teams are entered sorted, then the list will always be sorted. – Dean Leitersdorf Jul 02 '14 at 23:01
You can use a `PriorityQueue` instead. – Luiggi Mendoza Jul 02 '14 at 23:02
As for List#addAll(Collection) -- addTeams does not do that -_- – Dean Leitersdorf Jul 02 '14 at 23:02
@LuiggiMendoza interesting. how so? EDIT: You just place the elo score as a priority. Yes so its very similar to what I did. – Dean Leitersdorf Jul 02 '14 at 23:02
Read about it: [`PriorityQueue`](http://docs.oracle.com/javase/8/docs/api/java/util/PriorityQueue.html). – Luiggi Mendoza Jul 02 '14 at 23:03
Still, for priority queue, you would need a comparator. – Dean Leitersdorf Jul 02 '14 at 23:03
Any sorting on custom objects needs a `Comparator` unless the class implements `Comparable`... – Luiggi Mendoza Jul 02 '14 at 23:05
@LuiggiMendoza yes, anytime you sort you have a comparitor. However, in some cases, like this, you don't have to specify a comparitor in a seperate class -- the "comparitor" for my sorting above is teams.get(i).elo – Dean Leitersdorf Jul 02 '14 at 23:11

Java - Sorting Arraylist by an objects instances.

1 Answers1