Help comparing float member variables using Comparators

Question

I am able to compare Strings fine, but would like to know how I can rank floating point numbers?

getChange() returns a String. I want to be able to sort descending. How can I do this?

UPDATE:

package org.stocktwits.helper;

import java.util.Comparator;

import org.stocktwits.model.Quote;

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());

        if (change1 < change2) return -1;
        if (change1 == change2) return 0; // Fails on NaN however, not sure what you want
        if (change2 > change2) return 1;
    }
}

I am getting the compile time error:

This method must return a result of type int    ChangeComparator.java   

Answer 1

You can compare floats with the basic arithmetic operators, e.g. < or >.

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

Answer 2

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 (change2 > change2) return 1;
return 0;

Or if you like conditional operators:

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

Answer 3

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);
    }
}