Question

Im trying to sort through an arraylist of objects by a particular value within the object. What would be the best approach to do such a thing. Should I use Collections.sort() with some kind of comparator?

Im trying to sort a list of objects by a float value they hold in one of the variables.

EDIT:
This is what I have so far:

public class CustomComparator implements Comparator<Marker> {
    @Override
    public int compare(Mark o1, Mark o2) {
        return o1.getDistance().compareTo(o2.getDistance());
    }
}

the error states: Cannot invoke compareTo(double) on the primitive type double.

Is it because a comparator cant return anything other than a certain type?

Answer 1

You should use Comparable instead of a Comparator if a default sort is what your looking for.

See here, this may be of some help – When should a class be Comparable and/or Comparator?

Try this –

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class TestSort {

    public static void main(String args[]){

        ToSort toSort1 = new ToSort(new Float(3), "3");
        ToSort toSort2 = new ToSort(new Float(6), "6");
        ToSort toSort3 = new ToSort(new Float(9), "9");
        ToSort toSort4 = new ToSort(new Float(1), "1");
        ToSort toSort5 = new ToSort(new Float(5), "5");
        ToSort toSort6 = new ToSort(new Float(0), "0");
        ToSort toSort7 = new ToSort(new Float(3), "3");
        ToSort toSort8 = new ToSort(new Float(-3), "-3");

        List<ToSort> sortList = new ArrayList<ToSort>();
        sortList.add(toSort1);
        sortList.add(toSort2);
        sortList.add(toSort3);
        sortList.add(toSort4);
        sortList.add(toSort5);
        sortList.add(toSort6);
        sortList.add(toSort7);
        sortList.add(toSort8);

        Collections.sort(sortList);

        for(ToSort toSort : sortList){
            System.out.println(toSort.toString());
        }
    }

}

public class ToSort implements Comparable<ToSort> {

    private Float val;
    private String id;

    public ToSort(Float val, String id){
        this.val = val;
        this.id = id;
    }

    @Override
    public int compareTo(ToSort f) {

        if (val.floatValue() > f.val.floatValue()) {
            return 1;
        }
        else if (val.floatValue() <  f.val.floatValue()) {
            return -1;
        }
        else {
            return 0;
        }

    }

    @Override
    public String toString(){
        return this.id;
    }
}