How to sort ArrayLists?

Question

I have some lists that contain elements of type DataTime( Joda-time ). How can I sort them by date? It will be great if somebody gave link to the example...

Look into `Collections.sort` and `Comparator`. – nkr Oct 10 '12 at 21:05 — nkr, Oct 10 '12 at 21:05
@nkr I think you mean Comparator – Jordan Kaye Oct 10 '12 at 21:06 — Jordan Kaye, Oct 10 '12 at 21:06
Can you show the outline of the code? – Stas0n Oct 10 '12 at 21:07 — Stas0n, Oct 10 '12 at 21:07

arshajii · Accepted Answer · 2012-10-10T21:25:06.867

9

Because the objects of your list implement the Comparable interface, you can use

Collections.sort(list);

where list is your ArrayList.

Relevant Javadocs:

Edit: If you want to sort a list of a custom class that contains a DateTime field in a similar way, you would have to implement the Comparable interface yourself. For example,

public class Profile implements Comparable<Profile> { 
    DateTime date;
    double age; 
    int id; 

    ...

    @Override
    public int compareTo(Profile other) {
        return date.compareTo(other.getDate());  // compare by date
    }
}

Now, if you had a List of Profile instances, you could employ the same method as above, namely Collections.sort(list) where list is the list of Profiles.

edited Oct 10 '12 at 21:25

answered Oct 10 '12 at 21:06

arshajii

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And what if the ArrayList contains objects of class Profile public Profile{ DateTime date; Double age; int id; } How can i sort it by date? – Stas0n Oct 10 '12 at 21:13
1

Profile is a class, that i wrote myself – Stas0n Oct 10 '12 at 21:20

score 6 · Answer 2 · edited Oct 13 '12 at 13:43

6

DateTime already implements Comparable you just need to use Collections.sort()

edited Oct 13 '12 at 13:43

kleopatra

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answered Oct 10 '12 at 21:06

jmj

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And what if the ArrayList contains objects of class Profile public Profile{ DateTime date; Double age; int id; } How can i sort it by date? – Stas0n Oct 10 '12 at 21:16
1

You need to implement custom comparator in this case – jmj Oct 10 '12 at 21:16
1

@Stas0n see the edit on my post – arshajii Oct 10 '12 at 21:19
1

Could you show a sketch of the code? – Stas0n Oct 10 '12 at 21:20
1

http://stackoverflow.com/questions/5178092/sorting-a-list-of-points-with-java – jmj Oct 10 '12 at 21:21

How to sort ArrayLists?

2 Answers2