How to sort a collection by a date field?

I'm trying to sort an album by release date. For some reason I am not getting anywhere:

//sort by release date
Collections.sort(this._items, new Comparator<Album>() {
    public int compare(Album t1, Album t2) {
       开发者_如何学编程 int dateCmp = t2.getStartDate().compareTo(t1.getStartDate());
        Log.i("==Albums==", "dateComp: " + dateCmp);
        return t1.getStartDate().compareTo(t2.getStartDate());
    }            
});

What am I doing wrong?

Here is what I see in the output of Foo Fighters Albums by release date:

name: There Is Nothing Left To Lose | release date: 11/2/1999
name: Greatest Hits | release date: 11/3/2009
name: Skin And Bones | release date: 11/7/2006
name: Foo Fighters | release date: 12/10/2003
name: DOA | release date: 12/13/2005
name: Rope | release date: 3/1/2011
name: The Colour And The Shape | release date: 3/30/2010

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It look like that your startDate field is of type java.lang.String. At least, the order in the output confirms that. The String#compareTo() will order String values lexicographically, not by the value it represents in the eye of the beholder.

If you change the incorrect type to be java.util.Date, or use SimpleDateFormat#parse() to convert the String to Date inside the compare() method and then call Date#compareTo() instead, then the ordering will work as expected.

I'd replace it by java.util.Date. Always use the right type for the value it represents.

---

Here is the full code. The issue was because the start date was of type string.

//sort by release date

Collections.sort(this._items, new Comparator<Album>() {    
                        public int compare(Album t1, Album t2) {

                            int dateCmp = 0;

                             try {  

                                SimpleDateFormat formatter; 
                                Date date1; 
                                Date date2; 
                                formatter = new SimpleDateFormat("dd/mm/yyyy");

                                date1 = (Date)formatter.parse(t1.getStartDate()); 
                                date2 = (Date)formatter.parse(t2.getStartDate()); 

                                dateCmp = (date2).compareTo(date1);

                              } 
                              catch (Exception e)
                              {
                                //Log.i("==Albums==", "album special sort - error" );
                              }

                            //Log.i("==Albums==", "dateComp: " + dateCmp);

                            return dateCmp; 

                        }               
                    });