Sorting Collections

[Jade Lucky]

Hi ,
I came across this when I try to practice the example in SCJP 5.0 Study Guide by Kathy and I added some lines to is as well.

Program:-
ArrayList <String> test=new ArrayList<String>();
String s="hi";
test.add(s);
test.add("String");
test.add("EEE");
test.add("ABC");
System.out.println(test);
Collections.sort(test);
System.out.println(test);

and this is the output I get

[hi, Sting, EEE, ABC]
[ABC, EEE, Sting, hi]

Do any of you guys no the answer for this?

Cheers,
J

[Brian Legg]

De, I'm not sure what your question is. It seems you have some code and it is behaving as expected so what are you wanting it to do?

[Henry Wong]

Do any of you guys no the answer for this?

Strings are sorted based on unicode values. For letters and numbers, it is the same as the ASCII values. In the first printout, it is unsorted. In the second, it is sorted.

Henry

[Jelle Klap]

It has to do with the way the String.compareTo() method has been implemented. Basically the natural order imposed by the compareTo() implementation is based on the Unicode value of the individual characters in the String. The unintuitive (non-alphabetical) ordering of the output of your code sample is simply the result of upper case characters preceeding lower case characters.
If you want take character case out of the equation when sorting the List, you could either make sure the List only contains lower case or upper case Strings, or sort the List using a Comparator implementation that makes use of the String.compareToIgnoreCase() method.

Edit: Must. Type. Faster.
[ December 02, 2008: Message edited by: Jelle Klap ]

[Jade Lucky]

Hi guys thanks for quick reply ,
The first println prints unsorted collection while second one prints sorted one.This the output I get
[ABC, EEE, Sting, hi]

what I meant was it should be sorted as
[ABC, EEE, hi,Sting]

Because I have used
String s="hi" ,its not sorting properly.

Do you have any inkling what can be the reason for this?

Thanks.
D

[Brian Legg]

The capital 'S' comes before the lowercase 'h' in unicode values, so it will come before "hi". Take Jelle's suggestion to use a Comparator using the String.compareToIgnoreCase() method if you want the output to be in alphabetic order regardless of upper/lowercase.

[Jade Lucky]

Hi Jelle,
Thanks for the reply.

It works.

Cheers,
De