Sheehan Alam Sheehan Alam - 2 months ago 9
Java Question

Help comparing float member variables using Comparators

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

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?