How to sort ArrayLists? [duplicate]

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
– nkr

2012-10-10 21:05:43 +00:00
Commented Oct 10, 2012 at 21:05 — nkr
– nkr, Commented Oct 10, 2012 at 21:05
@nkr I think you mean Comparator

Jordan Kaye
– Jordan Kaye

2012-10-10 21:06:07 +00:00
Commented Oct 10, 2012 at 21:06 — Jordan Kaye
– Jordan Kaye, Commented Oct 10, 2012 at 21:06
Hint: sort by timestamp.

jn1kk
– jn1kk

2012-10-10 21:06:18 +00:00
Commented Oct 10, 2012 at 21:06 — jn1kk
– jn1kk, Commented Oct 10, 2012 at 21:06
Can you show the outline of the code?

Stas0n
– Stas0n

2012-10-10 21:07:58 +00:00
Commented Oct 10, 2012 at 21:07 — Stas0n
– Stas0n, Commented Oct 10, 2012 at 21:07

arshajii · Accepted Answer · 2012-10-10 21:25:06Z

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.