Sorting a double value of an object within an arrayList

Question

I\'m trying to sort my custom class chromosome by the value of their score attribute which is a double. These chromosomes are stored within an ArrayList. I know I have to us

Answer 1

I would implement the interface Comparable:

public class Chromosome implements Comparable{

    private double score;

    public Chromosome(double score){
        this.score = score;
    }
    @Override
    public int compareTo(Chromosome o) {
        return new Double(score).compareTo( o.score);
    }
    @Override
    public String toString() {
        return String.valueOf(score);
    }
}

Note that i moved score inside the Class..

Now you can use any Collection that is Sorted (like a TreeSet)

If you insist on using the Arraylist you can use:

ArrayList out = new ArrayList();
out.add(new Chromosome(20));
out.add(new Chromosome(15));
System.out.println(out);
Collections.sort(out);
System.out.println(out);

Result:

[0.2, 0.15]
[0.15, 0.2]