Help comparing float member variables using Comparators

How about this:

public class ChangeComparator implements Comparator<Quote>
{
    public int compare(Quote o1, Quote o2) {
        Float change1 = Float.valueOf(o1.getChange());
        Float change2 = Float.valueOf(o2.getChange());
        return change1.compareTo(change2);
    }
}

Note that Java 1.4 introduced Float#compare(float, float) (and an equivalent in Double), which can be pretty much used directly:

public class ChangeComparator implements Comparator<Quote>
{
    public int compare(Quote o1, Quote o2) {
        return Float.compare(o1.getChange(), o2.getChange());
    }
}

(After editing, I notice that @BorislavGizdov has mentioned this in his answer already.)

---

Also worth noting that Java 8 Comparator#comparing(...) and Comparator#comparingDouble(...) provide a straightforward way of constructing these comparators directly.

Comparator<Quote> changeComparator = Comparator.comparing(Quote::getChange);

Will compare using boxed Float values.

Comparator<Quote> changeComparator = Comparator.comparingDouble(Quote::getChange);

Will compare using float values promoted to double values.

Given that there is no Comparator#comparingFloat(...), my preference would be to use the comparingDouble(...) method, as this only involves primitive type conversion, rather than boxing.

Read the javadoc of Comparator#compare() method.

Compares its two arguments for order. Returns a negative integer, zero or a positive integer as the first argument is less than, equal to or greater than the second.

So, basically:

float change1 = o1.getChange();
float change2 = o2.getChange();
if (change1 < change2) return -1;
if (change1 > change2) return 1;
return 0;

Or if you like conditional operators:

return o1.getChange() < o2.getChange() ? -1 
     : o1.getChange() > o2.getChange() ? 1 
     : 0;

You however need to take account with Float.NaN. I am not sure how you'd like to have them ordered. First? Last? Equally?