Solved

Java Comparator - Sorting Question

Posted on 2008-06-17
7
1,103 Views
Last Modified: 2013-12-29
Hi All,

Below is a comparator that sorts numbers in ascending order starting with the smallest. I want to reverse this so that it sorts numbers in descending order, the largest number appearing first and so on.

Thanks for any help

public static Comparator myComparator  = new Comparator(){
            
            public int compare(Object value1, Object value2) {
                  String sVal1 = ((value1Entity)value1)getValue();
                  String sVal2 = ((value1Entity)value2)getValue();
            
            int iVal1 = 0;
            int iVal2 =0;
           
                  try { iVal1=(int)Float.parseFloat(sVal1); }
                    catch(NumberFormatException e) { }
                  try { iVal2=(int)Float.parseFloat(sVal2); }
                    catch(NumberFormatException e) { }             
                  
                if(iVal1 == 0)
                      iVal1 = 9999;
                if(iVal2 == 0)
                      iVal2 = 9999;
                    
                  if(iVal1<iVal2)
                        return 1;
                  else if(iVal2<iVal1)
                        return -1;
                  else //(iVal2==iVal1)
                        return 0;
            }
      };
0
Comment
Question by:laptopcomputer
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
7 Comments
 
LVL 86

Expert Comment

by:CEHJ
ID: 21804891
Just reverse iVal1 and iVal2 in the code
0
 

Author Comment

by:laptopcomputer
ID: 21805616

That does'nt seem to be working, where in the code do you replace ?

Thanks
0
 
LVL 86

Expert Comment

by:CEHJ
ID: 21805685
In the if-else section
0
Salesforce Has Never Been Easier

Improve and reinforce salesforce training & adoption using WalkMe's digital adoption platform. Start saving on costly employee training by creating fast intuitive Walk-Thrus for Salesforce. Claim your Free Account Now

 
LVL 11

Accepted Solution

by:
spoxox earned 250 total points
ID: 21805727
This compare method describes how to look at two objects and decide which is greater than the other. Some sort method (not shown) will rely on this compare method in order to sort several of these objects (two at a time).

When writing a compare method, you decide what you want to measure in order to decide the "greater than/less than" relationship. If your objects are cars, you might decide to use speed (car1.maxSpeed > car2.maxSpeed). If your objects are shirts, you might decided to use sizes (if(shirt1.size == "XXL" && shirt2.size == "XL") return 1).

In this case, you're taking an int representation...
...of a String representation....
...of the object, and comparing that.

You decided if iVal1 < iVal2 return 1.

To sort descending, rather than ascending, you can change your sort or your compare. You've chosen to change the compare.

So your compare method (comparator) must answer opposite to before - it's telling which (of two) is larger, not which is smaller.

So reversing
if (iVal1 < iVal2) return 1

will yield either
if(iVal2 < iVal1) return 1 // per CEHJ

or
if(iVal1 > iVal2) return 1


Make sense?
0
 
LVL 86

Expert Comment

by:CEHJ
ID: 21805776
Once you've got the values into iValX you can just do the following in fact instead of the if-else, and give yourself a  means of boolean flagging the reverseSort
return reverseSort? (iVal2 - iVal1) : (iVal1 - iVal2);

Open in new window

0
 
LVL 92

Expert Comment

by:objects
ID: 21808164
You don't need to do that. Don't complicate your comparator with reverse order, instead create a new comparator using the following

Comparator reverse = Collections.reverseComparator(myComparator);

0
 

Expert Comment

by:gunacesun
ID: 21816396
All that you have to do is after running your original comparator (one that returns a list in ascending order),
do a
Collections.reverse(list);

where list is the output of the original comparator.
0

Featured Post

[Live Webinar] The Cloud Skills Gap

As Cloud technologies come of age, business leaders grapple with the impact it has on their team's skills and the gap associated with the use of a cloud platform.

Join experts from 451 Research and Concerto Cloud Services on July 27th where we will examine fact and fiction.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Java had always been an easily readable and understandable language.  Some relatively recent changes in the language seem to be changing this pretty fast, and anyone that had not seen any Java code for the last 5 years will possibly have issues unde…
Introduction This article is the last of three articles that explain why and how the Experts Exchange QA Team does test automation for our web site. This article covers our test design approach and then goes through a simple test case example, how …
Viewers learn about the third conditional statement “else if” and use it in an example program. Then additional information about conditional statements is provided, covering the topic thoroughly. Viewers learn about the third conditional statement …
Viewers will learn how to properly install Eclipse with the necessary JDK, and will take a look at an introductory Java program. Download Eclipse installation zip file: Extract files from zip file: Download and install JDK 8: Open Eclipse and …
Suggested Courses

623 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question