Comparator

[Sujatha Musunuri]

Following is a question from K&B mock exam.

import java.util.*;

class Comp2{
public static void main(String args[]){
String[] words = {"Good", "Bad", "Ugly"};

Comparator<String> best = new Comparator<String>(){
public int compare(String s1, String s2){
return s2.charAt(1) - s1.charAt(1);
}
};

Arrays.sort(words, best);
System.out.println(words[0]);
}
}

ANS: Good

I'm always confused with Comparator. I could not get what exactly the s2.charAt(1) - s1.charAt(1); will do. How exactly it'll reverse the list? If it reverses the list then the list should be {"Ugly", "Bad", "Good"}. In this case, the words[0] should be-- Ugly.

Anyone, pls. clarify this to me - How the output is 'GOOD'?

[ahmed yehia]

How exactly it'll reverse the list?

The Comparator interface doesnt explicitly reverse the collection or the array, instead it gives the ability to sort based on the implementation of the compare().

In your example, array 'words' is sorted in descending order based on the second character of the String elements.

[Burkhard Hassel]

Howdy,

for a normal (non-reversed) ordering you'll have to substract
s1 - s2

but here it it reverse because of
s2 - s1


and because the ordering is on the second letter (charAt(1)) the sequence would be
Good
Ugly
Bad


Yours,
Bu.
[ November 11, 2007: Message edited by: Burkhard Hassel ]

[Jesper de Jong]

Sujatha M, please check your private messages. You can see them by clicking My Private Messages.