Collection : Mapping The Objects

Question

Assume I have two Lists, one for Movies and another one for Genres. I want to map one or more Genres to one Movie and/or one or more Movies to one Genre. How would I do that?

Answer 1

The Java Map-interface is used to map objects to other objects. A Map<Movie, List<Genre>> assigns a List of Genres to a single Movie, a Map<Genre, List<Movie>> would do it the other way around.

If you want a 2-way-map, there is already a question for that

Answer 2

The collection you should be using is Map<String, List<String>>.

For mapping one or more genre to a movie, you should use: Map<movie, List<genre>>

And for mapping one or more movie to a genre, you should use: Map<genre, List<movie>>

Answer 3

I suppose...something like that:

Movie f = new Movie("fight club"); // for example..
List<Genre> genres = ...; 
genres.add(new Genre("comic"));
genres.add(new Genre("horror"));

Map <Movie,List<Genre>> movieGenres = new HashMap<Movie,List<Genre>>();

movieGenres.add(f,genres);

Answer 4

Using appropriate map implementation.

Map<String, MyObject> map = new HashMap<String, MyObject>();

I suggest you to look at Guava multimap

Multimap<String, String> multimap = ArrayListMultimap.create();
multimap.put("action", "rambo");
multimap.put("action", "terminator");
multimap.put("thriller", "rambo");

System.out.println(multimap.get("action"));
System.out.println(multimap.get("thriller"));