如何按日期对对象列表进行排序（Java 集合、列表<Object> )

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.A stValue.getValue(AstValue.java:163)....

Answer 1

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());
    }
});

Answer 2

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();

Answer 3

在 Java 8+ 中，它现在很简单：

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

Answer 4

You're using Comparators incorrectly.

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

Answer 5

你可以使用这个：

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

Answer 6

我会添加 Commons NullComparator 来避免一些问题......

Answer 7

Using Java 8 functionality it will be simpler.

syntax : LIST_NAME.sort(Comparator.comparing(INFO_CLASS::getMethod));

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