ArrayList sorting issue in Android -

i've arraylist of objects.

arraylist<item> blog_titles = new arraylist<item>(); 

i want sort arraylist in descending order of 1 of datamembers datetime value stored string (timestamp in code below).

public class blogitem implements item, comparable<blogitem> {      public final string id;     public final string heading;     public final string summary;     public final string description;     public final string thumbnail;     public final string timestamp;  // format:- 2013-02-05t13:18:56-06:00     public final string blog_link;      public blogitem(string id, string heading, string summary, string description, string thumbnail, string timestamp, string blog_link) {               this.id = id;         this.heading = heading;         this.summary = summary;         this.description = description;         this.thumbnail = thumbnail;         this.timestamp = timestamp;   // format:- 2013-02-05t13:18:56-06:00         this.blog_link = blog_link;     }      @override     public int compareto(blogitem o) {         // todo auto-generated method stub         return this.timestamp.compareto(o.timestamp);     }  } 

item generic interface:

public interface item {     // todo auto-generated method stub } 

now when i'm trying sort arraylist like:

collections.sort(blog_titles); 

i following error message:

bound mismatch: generic method sort(list<t>) of type collections not applicable arguments (arraylist<item>). inferred type item not valid substitute bounded parameter <t extends comparable<? super t>> 

how fix above error & correct approach sort arraylist in case ?

your blog_titles list list of item.

item not comparable, while blogitem is.

either declare blog_titles arraylist<blogitem>, or make item extend comparable