How to sort a List of objects by their date (java collections, List

Question

private List<Movie> movieItems = null;
public List<Movie> getMovieItems() {
    final int first = 0;
    if (movieItems == null) {
        getPagingInfo();
        movieItems = jpaController.findRange(new int[]{pagingInfo.getFirstItem(), pagingInfo.getFirstItem() + pagingInfo.getBatchSize()});
        Collections.sort(movieItems, new Comparator(){
           public int compare (Object o1, Object o2){
               Date d1 = movieItems.get(((Movie)o1).getMovieId()).getDate();
               Date d2 = movieItems.get(((Movie)o2).getMovieId()).getDate();
               if(d1.before(d2)){
                   movieItems.set(1, (Movie)o1);
                   movieItems.set(2, (Movie)o2);
               }
               return first;
           }
       });
    }
    return movieItems;
}

jpaController is bringing back 4 movies and is giving me the following

java.lang.ArrayIndexOutOfBoundsException: Array index out of range: 4 at java.util.Vector.get(Vector.java:694) at entitybeans.jsf.PeliculaController$1.compare(PeliculaController.java:260) at java.util.Arrays.mergeSort(Arrays.java:1270) at java.util.Arrays.sort(Arrays.java:1210) at java.util.Collections.sort(Collections.java:159) at entitybeans.jsf.PeliculaController.getPeliculaItems(PeliculaController.java:257) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597) at javax.el.BeanELResolver.getValue(BeanELResolver.java:302) at javax.el.CompositeELResolver.getValue(CompositeELResolver.java:175) at com.sun.faces.el.FacesCompositeELResolver.getValue(FacesCompositeELResolver.java:72) at com.sun.el.parser.AstValue.getValue(AstValue.java:116) at com.sun.el.parser.AstValue.getValue(AstValue.java:163)....

score 62 · Accepted Answer · edited May 17 '16 at 15:00

62

In your compare method, o1 and o2 are already elements in the movieItems list. So, you should do something like this:

Collections.sort(movieItems, new Comparator<Movie>() {
    public int compare(Movie m1, Movie m2) {
        return m1.getDate().compareTo(m2.getDate());
    }
});

edited May 17 '16 at 15:00

madhead

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answered Mar 05 '11 at 21:55

pwc

7,043
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19

it's `m1.getDate().compareTo(m2.getDate());` me think – Adriano Aug 20 '13 at 08:45
@AdrienBe, i think you are correct. pwc, please include adrien's suggestion in your answer. – Subham Tripathi Sep 24 '15 at 06:19
am using this code working fine. i need get data between two dates(start,end) from arraylist..how can i change that code? – sasikumar Sep 28 '15 at 14:00

Bozho · Answer 2 · 2011-03-05T22:01:55.433

Do not access or modify the collection in the Comparator. The comparator should be used only to determine which object is comes before another. The two objects that are to be compared are supplied as arguments.

Date itself is comparable, so, using generics:

class MovieComparator implements Comparator<Movie> {
    public int compare(Movie m1, Movie m2) {
       //possibly check for nulls to avoid NullPointerException
       return m1.getDate().compareTo(m2.getDate());
    }
}

And do not instantiate the comparator on each sort. Use:

private static final MovieComparator comparator = new MovieComparator();

riddle_me_this · Answer 3 · 2021-05-24T22:26:31.613

20

In Java 8+, it's now as simple as:

movieItems.sort(Comparator.comparing(Movie::getDate));

edited May 24 '21 at 22:26

answered Jul 28 '16 at 22:27

riddle_me_this

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Awesome! Thanks java8 and @bphilipnyc! – Camille Jul 03 '17 at 14:57

Stefan Kendall · Answer 4 · 2011-03-06T01:21:21.843

16

You're using Comparators incorrectly.

 Collections.sort(movieItems, new Comparator<Movie>(){
           public int compare (Movie m1, Movie m2){
               return m1.getDate().compareTo(m2.getDate());
           }
       });

edited Mar 06 '11 at 01:21

answered Mar 05 '11 at 21:55

Stefan Kendall

66,414
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2

But, `movieItems` is a list of `Movie` objects, not `Date` objects. – pwc Mar 05 '11 at 21:59

score 1 · Answer 5 · edited Mar 25 '15 at 16:27

1

You can use this:

Collections.sort(list, org.joda.time.DateTimeComparator.getInstance());

edited Mar 25 '15 at 16:27

msrd0

7,816
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answered Mar 25 '15 at 15:22

Damian Górski

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3

Joda is a large framework to import so unless you're using more functions from the framework, I would not recommend this method. – spogebob92 Feb 12 '16 at 11:06

score 1 · Answer 6 · answered Jan 24 '12 at 16:33

1

I'd add Commons NullComparator instead to avoid some problems...

answered Jan 24 '12 at 16:33

neeeeee

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How to sort a List of objects by their date (java collections, List

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